As described in T114621#1862046 by @Trondtr, it seems that under some circumstances the publish button does not become active making it impossible to publish a translation. Details copied below:

Here is the procedure:

I choose text + title for the translated article
I click the "Start a new translation"
The page I arrive at has the original to the left, an empty field to the right, and a grey "Publish translation" button
I click the paragraphs, one by one, and get translations from Apertium. Now, things go good or bad:
GOOD:
After my first click, I get translated text, and the grey button turn green. Now I know I may continue, I will be able to publish in the end.
BAD:
After my first click, I get translated text, but the grey button does NOT turn green. Now I know I have to abandon this translation. No matter what I do, I will not be able to translate on any point. The button will stay gray, and nothing will happend when I press the grey button.

No other error message turns up. The button either starts out gray and continues as gray, or it turns green when the first paragraph is translated (I imagine the program scans the text for errors)..