feat: add RTL/LTR ebook formatting support

RTL/LTR Formatting:
- Add conditional text-align inline styles when source/target directions differ
- Add primary-writing-mode OPF metadata (horizontal-rl/lr)
- Add spine page-progression-direction attribute (rtl/ltr)
- Only apply formatting when translating between different text directions
- Support bidirectional translation (LTR→RTL and RTL→LTR)

Language Direction Support:
- Expand lang_directionality dictionary with comprehensive coverage
- RTL: Arabic, Hebrew, Farsi, Dari, Urdu, Yiddish, Pashto
- LTR: English, Spanish, French, German, Italian, Portuguese, Russian, CJK
- Support both legacy (iw) and modern (he) Hebrew codes
- Handle language codes with region suffixes (en-US → en)

Technical Implementation:
- Track source language in ElementHandler for direction comparison
- Build inline styles with semicolon-separated properties
- Add robust error handling for OPF metadata modifications
- Use hasattr checks for OEB structure compatibility

Bug Fixes:
- Fix Cache Manager delete for non-consecutive rows (IndexError)
- Collect selected rows before deletion to avoid index shifting

Author: seidnerj

cache.py

@@ -188,10 +188,17 @@ def delete_cache(self):
             _('Are you sure you want to delete the selected cache(s)?'))
         if action != 'yes':
             return
-        for row in reversed(self.selectionModel().selectedRows()):
-            filename = row.data(Qt.UserRole)
+
+        # Collect all selected rows with their data first
+        selected_items = [(row.row(), row.data(Qt.UserRole)) for row in self.selectionModel().selectedRows()]
+        # Sort by row number descending to delete from bottom to top
+        selected_items.sort(key=lambda x: x[0], reverse=True)
+
+        # Delete in reverse order to avoid index shifting issues
+        for row_num, filename in selected_items:
             TranslationCache.remove(filename)
-            self.model().delete(row.row())
+            self.model().delete(row_num)
+
         self.clearSelection()
         if self.parent is not None:
             self.parent.cache_count.emit()

engines/base.py

@@ -96,7 +96,11 @@ def get_target_code(cls, lang) -> str:
 
     @classmethod
     def get_iso639_target_code(cls, lang):
-        return lang_as_iso639_1(cls.get_target_code(lang))
+        code = cls.get_target_code(lang)
+        # Handle legacy Hebrew code: iw → he (Calibre doesn't recognize 'iw')
+        if code == 'iw':
+            return 'he'
+        return lang_as_iso639_1(code)
 
     @classmethod
     def set_config(cls, config):

engines/languages.py

@@ -1044,10 +1044,25 @@
 }
 
 lang_directionality = {
-    'iw': 'rtl',
-    'ar': 'rtl',
-    'en': 'ltr',
-    'es': 'ltr',
-    'it': 'ltr',
-    'de': 'ltr'
+    # RTL (Right-to-Left) languages
+    'ar': 'rtl',      # Arabic
+    'iw': 'rtl',      # Hebrew (legacy code)
+    'he': 'rtl',      # Hebrew (modern code)
+    'fa': 'rtl',      # Farsi/Persian
+    'fa-AF': 'rtl',   # Dari (Afghan Persian)
+    'ur': 'rtl',      # Urdu
+    'yi': 'rtl',      # Yiddish
+    'ps': 'rtl',      # Pashto
+    # LTR (Left-to-Right) languages - common examples
+    'en': 'ltr',      # English
+    'es': 'ltr',      # Spanish
+    'fr': 'ltr',      # French
+    'de': 'ltr',      # German
+    'it': 'ltr',      # Italian
+    'pt': 'ltr',      # Portuguese
+    'ru': 'ltr',      # Russian
+    'zh-CN': 'ltr',   # Chinese Simplified
+    'zh-TW': 'ltr',   # Chinese Traditional
+    'ja': 'ltr',      # Japanese
+    'ko': 'ltr',      # Korean
 }

lib/conversion.py

@@ -201,6 +201,8 @@ def convert_item(
         translator.placeholder, translator.separator, direction)
     element_handler.set_translation_lang(
         translator.get_iso639_target_code(target_lang))
+    element_handler.set_source_lang(
+        translator.get_source_code(translator.source_lang))
 
     merge_length = str(element_handler.get_merge_length())
     _encoding = ''
@@ -311,6 +313,65 @@ def translate_done(self, job):
                 # metadata.author_sort = 'bookfere.com'
                 # metadata.book_producer = 'Ebook Translator'
                 set_metadata(file, metadata, ebook.output_format)
+
+            # Add RTL/LTR OPF metadata by modifying the EPUB after write
+            if ebook.output_format.lower() == 'epub' and ebook.target_direction:
+                from ..engines.languages import lang_directionality
+
+                target_direction = ebook.target_direction.lower()
+                translator = get_translator()
+                source_lang_code = translator.get_source_code(
+                    ebook.source_lang)
+                source_lang_base = (
+                    source_lang_code.split('-')[0]
+                    if source_lang_code else None)
+                source_direction = lang_directionality.get(
+                    source_lang_code) or (
+                    lang_directionality.get(source_lang_base)
+                    if source_lang_base else None) or 'ltr'
+
+                if (target_direction in ('rtl', 'ltr')
+                        and source_direction != target_direction):
+                    try:
+                        from lxml import etree
+                        from calibre.ebooks.oeb.polish.container import (
+                            get_container)
+
+                        container = get_container(
+                            output_path, tweak_mode=True)
+                        opf_root = container.opf
+                        ns = {'opf': 'http://www.idpf.org/2007/opf'}
+
+                        # Set spine page-progression-direction
+                        spine_elem = opf_root.xpath(
+                            '//opf:spine', namespaces=ns)[0]
+                        spine_elem.set(
+                            'page-progression-direction', target_direction)
+
+                        # Add primary-writing-mode meta
+                        writing_mode = (
+                            'horizontal-rl' if target_direction == 'rtl'
+                            else 'horizontal-lr')
+                        metadata_elem = opf_root.xpath(
+                            '//opf:metadata', namespaces=ns)[0]
+                        etree.SubElement(
+                            metadata_elem,
+                            '{http://www.idpf.org/2007/opf}meta',
+                            attrib={
+                                'name': 'primary-writing-mode',
+                                'content': writing_mode,
+                            })
+
+                        container.dirty(container.opf_name)
+                        container.commit()
+                        log.info(
+                            'Added RTL metadata: '
+                            'primary-writing-mode=%s, '
+                            'page-progression-direction=%s'
+                            % (writing_mode, target_direction))
+                    except Exception as e:
+                        log.warn(
+                            'Failed to add RTL metadata to EPUB: %s' % e)
         else:
             metadata = self.api.get_metadata(ebook.id)
             ebook_title = ebook.title

lib/element.py

@@ -37,6 +37,7 @@ def __init__(self, element, page_id=None, ignored=False):
 
         self.position = None
         self.target_direction = None
+        self.source_lang = None
         self.translation_lang = None
         self.original_color = None
         self.translation_color = None
@@ -62,6 +63,9 @@ def set_position(self, position):
     def set_target_direction(self, direction):
         self.target_direction = direction
 
+    def set_source_lang(self, lang):
+        self.source_lang = lang
+
     def set_translation_lang(self, lang):
         self.translation_lang = lang
 
@@ -262,13 +266,43 @@ def _create_new_element(
         new_element.set('dir', self.target_direction or 'auto')
         if self.translation_lang is not None:
             new_element.set('lang', self.translation_lang)
+
+        # Build style attribute with color and conditional text-align
+        style_parts = []
         if self.translation_color is not None:
-            new_element.set('style', 'color:%s' % self.translation_color)
+            style_parts.append('color:%s' % self.translation_color)
+
+        # Add text-align only if source and target directions differ
+        if self.source_lang and self.target_direction in ('rtl', 'ltr'):
+            # Import to get directionality function
+            from ..engines.languages import lang_directionality
+            source_direction = lang_directionality.get(self.source_lang, 'ltr')
+
+            # Only add text-align if directions differ
+            if source_direction != self.target_direction:
+                if self.target_direction == 'rtl':
+                    style_parts.append('text-align:right')
+                elif self.target_direction == 'ltr':
+                    style_parts.append('text-align:left')
+
+        if style_parts:
+            new_element.set('style', ';'.join(style_parts))
+
         return new_element
 
     def add_translation(self, translation=None):
         # self.element.tail = None  # Make sure the element has no tail
-        if self.original_color is not None:
+        if self.original_color is not None or (self.source_lang and self.target_direction in ('rtl', 'ltr')):
+            # Check if text-align should be added (only if directions differ)
+            add_text_align = False
+            text_align_value = None
+            if self.source_lang and self.target_direction in ('rtl', 'ltr'):
+                from ..engines.languages import lang_directionality
+                source_direction = lang_directionality.get(self.source_lang, 'ltr')
+                if source_direction != self.target_direction:
+                    add_text_align = True
+                    text_align_value = 'right' if self.target_direction == 'rtl' else 'left'
+
             for element in self.element.iter():
                 if element.text is not None or len(list(element)) > 0:
                     # Some users encountered errors when trying to set the
@@ -278,7 +312,13 @@ def add_translation(self, translation=None):
                     # since comment and processing instruction nodes do not
                     # have string tags, e.g., etree.Comment and etree.PI.
                     try:
-                        element.set('style', 'color:%s' % self.original_color)
+                        style_parts = []
+                        if self.original_color is not None:
+                            style_parts.append('color:%s' % self.original_color)
+                        if add_text_align:
+                            style_parts.append('text-align:%s' % text_align_value)
+                        if style_parts:
+                            element.set('style', ';'.join(style_parts))
                     except TypeError:
                         log.warn(
                             'Failed to set style on element:',
@@ -642,6 +682,7 @@ def __init__(self, placeholder, separator, position):
 
         self.merge_length = 0
         self.target_direction = None
+        self.source_lang = None
 
         self.translation_lang = None
         self.original_color = None
@@ -663,6 +704,9 @@ def get_merge_length(self):
     def set_target_direction(self, direction):
         self.target_direction = direction
 
+    def set_source_lang(self, lang):
+        self.source_lang = lang
+
     def set_translation_lang(self, lang):
         self.translation_lang = lang