fix: Improve clarity around customizations' supported languages

[BriannaDelgado]

No description provided.

[shirgoldbird]

Closing as superseded, with the table work carried forward separately (see below).

Core concept — already documented, more thoroughly. The clarification this PR set out to make (glossaries and style rules are created for a root language but apply to its variants) is now covered by the dedicated guide How to Apply Customizations to Language Variants, plus inline notes in managing-glossaries.mdx and using-style-rules.mdx. The api-reference/translate.mdx edit here is also moot — that page was retired into an OpenAPI stub in #396.

Table badges — carried forward on top of #395. The one genuinely un-migrated piece is the language-table 'create vs. apply' badge distinction for variant rows. Since #395 makes snippets/language-table.jsx generated from GET /v3/languages (with a daily sync workflow), hand-editing the static array here would just be overwritten. The badge refinement is being reworked as a new PR stacked on #395 so it lives in the generator/badge component instead.

No action needed on this PR.