About it, the game is at latin spanish but if you had the game before the final version installed at epic store, it will not detect the new languages. Just it needs be reinstalled. Anyway, I claimed the steam key, I prefer steam because I use it with my other games as Sins of a Solar Empire Rebellion by example.

Hello! Just following up here, we've pushed a recent update to the Test Branch build of the game which includes a language selection option in the settings now 

To Change to Test Edition on Steam:

1. Select ‘Sins of a Solar Empire II’ in your Steam Library.

2. Click the gear icon in the upper right.

3. Select Properties → Betas

4. Select 'test_edition' from the Beta Participation dropdown.

5. Steam will update you to the latest files.

6. To switch back repeat step 4 and select ‘None’