The "Level Requirement" message on enchantment tables is hardcoded and cannot be translated, even though the rest of the enchantment table messages are.
To reproduce:
Acquire an enchantment table and an enchantable item.
Make sure you have no experience levels.
Switch language to ɥsᴉꞁᵷuƎ (ɯopᵷuᴉʞ pǝʇᴉu∩), as that language has a 100% translation (and is pretty easy to compare).
Put the enchantable item in the enchantment table.
Hover over one of the enchant buttons. The message "Level Requirement: 2" (or similar) should be displayed in red, untranslated.
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Yes, as is the "Enchantment Cost" message on the anvil GUI.
Still an issue in 16w44a
Is "Too Expensive" on the anvil GUI translatable?