library should be changed to media library in core or needs gettext

[timse201]

​https://translate.wordpress.org/projects/wp/dev/de/default/?filters%5Bstatus%5D=either&filters%5Boriginal_id%5D=16513323&filters%5Btranslation_id%5D=115284524

library is used for media library and for Gutenberg libraries. We have a single short word in German for media library that differs.

[audrasjb]

To be clear, what is needed here is a context for translators, using the _x() function.
See ​https://developer.wordpress.org/plugins/internationalization/how-to-internationalize-your-plugin/#disambiguation-by-context

## Summary

The string "Library" was used in two unrelated contexts without translator context:

• As the Media Library submenu item in the admin menu
• As the installed fonts tab label in the Font Library page

In languages like German, these concepts use different words (Mediathek vs. Bibliothek), making a single translation impossible without disambiguation.

## Changes

• wp-admin/menu.php: Changed __( 'Library' ) to _x( 'Library', 'Media Library menu item' ) for the Media submenu entry.
• wp-includes/build/routes/font-list/content.js and content.min.js: Changed __("Library") to _x("Library", "Font library") for the installed-fonts tab title, aligning it with the already-correct _x() usage in the Font Library modal.

## Testing

No functional change in English. Translators can now provide distinct translations for each context via _x().

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Trac ticket: https://core.trac.wordpress.org/ticket/64982

[audrasjb]

This fixes the issue, but I'd rather add a context for both strings.