cannot edit the language of the question

The restriction kinda make sense to me. Since you can't speak that language, you shouldn't be able to edit the question language to some other language you don't speak. In your example, what language would you set it to? portuguese or spanish? So, I think it's better to leave it as english and let someone who speaks spanish or portuguese to make an informed decision. What do you think?

Many times you can recognise the language even if you don't speak it, or if you do but didn't set it up as a language that you wish to receive questions in.
Ie. I can recognize german even though I don't speak it.
In my example question I would set it to spanish (now I saw that the description contains " LANG=gl_ES.UTF-8", also I've made myself sure using Google Translate).

Indeed I have experienced this problem when correcting the direction of RTL languages. I fixed the question by changing my preferred languages.

I think an answer contact should be permitted to set it to any language. I am confident I can identify many languages that I cannot claim to speak. An answer contact may be guessing at the language, but I expect him or her to act responsibly. I don't think keeping the question as the language we know it is not does not help get it answered.

I think this is a legitimate problem that we can fix.

I'm setting this to low since this is not happening often, and there is a way to fix this my tinkering with your preferred languages. None-the-less, answer contacts should be able to choose from all languages when editing the question.

Fixed released in launchpad-project 3.1.12.