(In reply to comment #0)

If a registered user has done already translations to e.g. Catalan, whenever
she clicks "Translate this page" it should land on a page ready to start
translating in Catalan.

Sounds reasonable. I am moving it to the Translate extension, because it's not a bug in ULS, but a matter of how Translate uses ULS.

• English appears as default language for translation, when clearly that is

the
less likely option.

Definitely.

• Iñupiak, ᏣᎳᎩ or Hawai`i appear at the top in "Common languages" (really???)

I guess that you are trying to do this in the US, and according to the CLDR these are the common languages of the US. The mysterious ᏣᎳᎩ language is Cherokee. If you would do this from an IP in Spain, Catalan would appear there.

CLDR is the default, but making the defaults smarter is what this bug is about.

and every time I need to type Catalan to select one of the languages that
matter in my wiki.

It should basically remember your latest selected languages.

@Qgil We basically use the interface language as default. Is that not acceptable to you? If we use some other mechanism, the language selection could look random to the user.

The only thing that is still strange is to be offered English as language for translation when the source page is in English. If possible, the selection could go like this:

1. Last language the user selected for translation.
2. If that information is not available, then interface language when other than English.
3. If the interface is in English, first recommendation from Common languages.

Yes we could, but is there enough benefit? In general people do not seem to pay attention what language is selected, as seen by the frequent number of cases when they accidentally Translate in qqq or some other wrong language. I think the current practice mitigates that issue to some extend and your suggestion would make that issue more prominent.

Right now we are forcing users to explicitly select a language when our guess matches the source language: https://www.mediawiki.org/w/index.php?title=Special:Translate&group=page-Help%3AExtension%3ATranslate%2FInstallation&action=page&filter=&uselang=en

Thank you for the explanations. Feel free to decline this task. I agree that it is not an urgent/important matter, and the alternatives might bring their problems as well.