[uom] Add Celsius, Fahrenheit and other UoM single glyph aliases

[andrewfg]

There is confusion between the two character symbol adopted by OH for Celsius °C (which is the official standard) and the one character symbol ℃ (which is a compatibility glyph for East Asian languages). This PR hopes to fix it. But I would like OH maintainers to please give feedback over the proposed solutions. And there is the same issue for Fahrenheit, and some other units..

Signed-off-by: Andrew Fiddian-Green software@whitebear.ch

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What the AI says about temperature symbols

The internationally accepted SI symbol is unequivocally “°C”.
The single-character symbol “℃” is not an SI‑approved symbol — it is a Unicode compatibility glyph used mainly in East Asian typography.

📌 What the standards say

• The SI derived unit for Celsius temperature is degree Celsius, symbol °C.
  This is explicitly defined in SI documentation: “degree Celsius °C” [European Patent Office](https://www.epo.org/en/legal/guidelines-epc/2025/f_iia2_1_1_1.html).
• Authoritative scientific references (e.g., NIST, Wikipedia’s SI‑aligned entry) also use °C exclusively as the symbol for Celsius. [Wikipedia](https://en.wikipedia.org/wiki/Celsius)

Why “℃” is not the standard

• ℃ (Unicode U+2103) is a compatibility symbol included for legacy East Asian typesetting.
• It is not recognised by SI, not used in scientific publications, and not recommended for technical writing, standards, or instrumentation.

Bottom line

• Correct SI symbol: °C
• Avoid: ℃ (non‑standard, typographic convenience only)

If you want, I can also tell you which environments or fonts render “℃” poorly and why it’s avoided in engineering contexts.

[andrewfg]

Ping @htreu

[dilyanpalauzov]

bundles/org.openhab.core.model.script/src/org/openhab/core/model/script/Script.xtext contains:

COMMON_UNIT_SYMBOLS:
    '°C' | '°F' | 'Ω' | '℃' | '°' | '%' | 'm²' | 'm³'

It does not contain ㎡.

Nobody has asked for ㎡, so probably it is also not necessary.

[andrewfg]

@dilyanpalauzov thanks for the feedback but excuse me for asking again to be clear .. which characters do you think shall be, and shall not be, added to this PR? From your prior post maybe you are suggesting to add at least the Ω symbol ?? .. but you are suggesting that none of the East Asian single character glyphs for Roman multi character symbols ㎏ ㎡ ㎥ ㎜ ㎝ ㎞ ㏈ shall be included. Or??

EDIT: I think Ω is already inherited from the Indriya library..

[dilyanpalauzov]

I am drawing the attention that Script.xtext also has handling of special characters, used as units. I am not suggesting anything.

[andrewfg]

Script.xtext also has handling of special characters

Do you know what is the purpose of Script.xtext?

[mherwege]

Script.xtext also has handling of special characters

Do you know what is the purpose of Script.xtext?

Parsing DSL scripts, rule bodies and DSL transformations.

[mherwege]

LGTM