Complete EU language translations to 100% coverage

[cat5inthecradle]

Blocked on: #421 (i18n locale support) must merge first.

Problem

Of the 24 official EU languages, only English has 100% translation coverage. 5 languages are essentially untranslated stubs, and 1 is partial:

Language	Locale	Keys	Coverage	Issue
Maltese	mt_mt	1/107	1%	Stub — only 1 key translated
Estonian	et_ee	7/107	7%	Stub
Latvian	lv_lv	7/107	7%	Stub
Lithuanian	lt_lt	7/107	7%	Stub
Danish	da_dk	10/107	9%	Stub
Slovenian	sl_si	94/107	88%	Partial — missing UI labels (colors, buttons)

The remaining 17 non-English EU languages are at 97-98%, each missing only the 3 recently added keys:

• training-generic-please-continue
• switchToMatchingItems
• switchToNonMatchingItems

Goal

Get all 24 EU languages to 100% coverage (107/107 keys).

Work involved

1. Small lift (17 languages): Translate the 3 missing keys for Bulgarian, Croatian, Czech, Dutch, Finnish, French, German, Greek, Hungarian, Irish, Italian, Polish, Portuguese, Romanian, Slovak, Spanish, and Swedish.
2. Medium lift (1 language): Translate the 13 missing keys for Slovenian.
3. Large lift (5 languages): Full translations needed for Danish (97 keys), Estonian (100 keys), Latvian (100 keys), Lithuanian (100 keys), and Maltese (106 keys).

Context

These translations are sourced from the main code-dot-org/code-dot-org monorepo (apps/i18n/fish/). The stub files likely represent languages that were added to the translation pipeline but never completed upstream. Completing them upstream and re-syncing (via yarn sync-i18n) would be the preferred path.

See PR #421 for the i18n locale support implementation.