Fixed ReferenceError caused by undefined lang variable in i18next

[ssz2605]

Description

This PR fixes a runtime ReferenceError caused by an undefined lang variable during i18next initialization.

The application previously called i18next.changeLanguage(lang, ...) without defining lang, which resulted in a console error and interrupted the language initialization flow.

Changes Made

Defined a default language ("en") before calling i18next.changeLanguage

Ensured the language change occurs only after i18next is successfully initialized

Expected Behavior

The application initializes i18next without throwing any runtime errors, and translations load correctly using the default language.

closes #4946

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[ssz2605]

@walterbender I ran npm run lint and npx prettier --check locally and both pass without any issues.

The ESLint failure in CI seems to be related to the workflow trying to lint a file path that doesn’t resolve correctly in the GitHub Actions environment (Linux), not due to a linting or formatting error in this PR’s code.

[walterbender]

Were you testing from a local server or directly from the file system? I tried the latter with Firefox:

before your change

MB launches nonetheless.

after your change

MB does not launch

Any ideas?

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[ssz2605]

@walterbender Yes I was testing on local server , maybe the issue was that my earlier code made i18next initialization blocking. When locales/en.json failed to load over file://, the promise never resolved, so MB never reached requirejs(["utils/utils", "activity/activity"]). I’ve updated the code so i18next always resolves (errors are logged), restoring the old behavior. Could you please check if MB is opening now?