Implement language selector in extension settings

[neshumov]

Issue Details

Currently extension’s interface language is determined automatically based on browser language. Users whose browser language differs from their native language have no way to choose a more convenient interface language. This negatively affects user experience.

Proposed solution

Implement separate Language option appears in extension settings where user can select interface language from the list of available languages.
Changes are applied immediately after selection (no browser or extension restart required).
By default language is still determined automatically based on browser language but user can override it manually.

Alternative solution

No response