Sorry for rehashing this, but I think I chose the wrong title (and angle) and it didn’t get the proper attention.
Right now, Discourse is incompatible with Google Translate which is likely the most used translation tool.
Any topic URL pasted into Google Translate always ends up with the 404 page being translated and not the actual topic. It works ok with the homepage and topic lists URLs – but not a topic.
Perhaps Google Translate is being fed some special crawler/print version that doesn’t work for this purpose?
I use Google Translate regularly and I only saw this behaviour with Discourse topics, so at least part of the issue appears to be in Discourse.