Difficult, as I asked my husband for the meaning. It is very context dependant. By itself you can use it to mean "They are on number eleven...of the quiz" "They are on number eleven....Blaba Street." "They are on number eleven...for the queue"
Hmm...in that case, I think "in/at" should also be accepted alongside "on".
I also think "at" should be accepted. Like when commenting on ranking. "My website is at number eleven on Google", "My song is at number eleven in the charts", etc.
That is how they say it -- they are in eleventh place or they are in the eleventh position. Personally, I like to see literal translations as it helps with my understanding of the grammar and how people talk about things. Language is never always literally translatable, each has quirks. The trick is to understand what this phrase means in context. What is missing here is the context -- which is why we have these comments :-)
It's not clear what this means. On train number eleven? That's the only thing that comes to mind.