This sounds like a feature request with one single use case (which requires having one specific extension installed)?

I believe characterising this as a feature request with one single use case does not do it justice. Page Previews are completely broken when the Translate extension is installed. For example, hover over any link in mediawiki.org/wiki and you get a useless Spcial:MyLanguage pop-up. Compare this with Wikipedia where you generally get a highly informative page preview.

Both translation and page previews are essential features for us and a temporary work-around (assuming the root cause shows no sign of being fixed) would be the ability to optionally disable the insertion of Special:MyLanguage prefixes to internal links on preparation of a page for translation.

Pleriche: Thanks for the elaboration! That helped a lot to understand the impact.

@Pleriche, well you can always get better results by preparing a page for translation manually. The special page is rather a convenience feature...

@Base: Well you could, but you need an excellent understanding of how the Translation Unit tags work and the ability to insert them without error. But I assume you might also have to manually hack the database to mark the page as available for translation - definitely not a good idea.

Equally, with less effort and less liklihood of error, you can manually take out the Special:Mylanguage prefixes after preparing a page for translation. But if some eager beaver has already started translating the page into a language you don't understand before you notice, this gets harder.

In T341080#8993086, @Pleriche wrote:

@Base: Well you could, but you need an excellent understanding of how the Translation Unit tags work and the ability to insert them without error.

Actually, with a little practice, I think one’s able to prepare a page at a much higher quality than with the special page. In my experience, the special page more often gets it wrong than right.

But I assume you might also have to manually hack the database to mark the page as available for translation - definitely not a good idea.

No, manual hacking of the database is not necessary. All this special page does is inserting the markup and saving the page – you could do this using action=edit as well. The “Mark this page for translation” link appears because of the <translate> tags, not because of using the special page. Inserting the tags manually also makes the link appear.

@Tacsipacsi : Thank you, that's interesting to know - it would have taken me for ever to ascertain that with any certainty from the doumentation. But what about the /en versions of pages that appear - do they serve any useful purpose?

If it were my day job I might follow your lead but for occasional use the special page is going to be less error prone. The only problem I've foud with it (apart from Special:MyLanguage) is that it tends to insert unwanted blank lines. But they're easily enough weeded out.

In T341080#8994613, @Pleriche wrote:

@Tacsipacsi : Thank you, that's interesting to know - it would have taken me for ever to ascertain that with any certainty from the doumentation. But what about the /en versions of pages that appear - do they serve any useful purpose?

This question is out of scope here – let’s continue on your mediawiki.org user talk page.