This might sound silly, but I like how LinkedIn Skills makes use of the active or inactive "+" next to each skill.

Imagine this UI (where "+" means active and "(+)" visible but inactive.

Aragonés (+)
العربية +
Asturianu (+)
Deutsch +
English +
Español +
Euskara +
Français +
Galego +

Turns out I don't understand العربية or Euskara, even if I clicked these languages sometimes just looking for something that today I don't remember. If I would click the + it would turn into (+), and perhaps from that moment they would lose weight compared to other languages I have visited but not evaluated in a way or another.

From what I understood so far, I think there are two different issues:

• The red links being a bit too distracting from the reading experience. There are other links crowding the sidebar that go unnoticed, but if there are some red links you don't want to use they are too hard to ignore.
• False positives added to the list. People that selected a language occasionally and it stays there forever.

I think that adding more controls to the list of links is not the best approach since it will add more clutter. I'd propose the following instead:

• Make the links grey (#777). They will still communicate that something is missing when you look at the language list wondering if the article is available in your language, but they won't get in the way of people not looking for languages.
• Once the panel is open provide an option to adjust the settings about translation recommendations. For example a drop-down with two options: "Don't suggest me translations to Bulgarian", and "Don't suggest me translations to any language". Those should prevent a specific missing language (or all of them) to be shown to the user.

I included a mockup illustrating the first change (which can be applied independently) and I'll add more details for the dialog changes.

Yes, I think the simple change to grey color will solve the urgency of this problem.

Change 207743 had a related patch set uploaded (by Santhosh):
Change the color of interlanguage entry points to grey

https://gerrit.wikimedia.org/r/207743

Change 207743 merged by jenkins-bot:
Change the color of interlanguage entry points to grey

https://gerrit.wikimedia.org/r/207743

Make the links grey (#777). They will still communicate that something is missing when you look at the language list wondering if the article is available in your language, but they won't get in the way of people not looking for languages.

This was done by @santhosh.

Once the panel is open provide an option to adjust the settings about translation recommendations. For example a drop-down with two options: "Don't suggest me translations to Bulgarian", and "Don't suggest me translations to any language". Those should prevent a specific missing language (or all of them) to be shown to the user.

This sounds reasonable. @Pginer-WMF, can you please make a mockup?

The Wikidata “Add links” link is featuring Base30 as grey color, but features a blue accent :hover state. Wondering if a desktop-first :hover missing language links Red50 should be considered?