Probably the same issue or cause as MC-184029. But without knowing the intended behavior it is difficult to quantify what is a bug and what isn't.

To reproduce:

1. Open the language menu
2. Click a language
3. Hit tab and observe that nothing changes

Or:

1. Open the language menu
2. Hit tab three times, the done button is now focused
3. Click a language with the cursor, the language entry is now focused and hitting enter will not activate the done button
4. Hit tab. Nothing changes visually, but the language entry is still focused - but hitting tab should have moved focus onto the next UI element, the force unicode button.