Nonsensical was probably not the right word—I should have focused simply on the lack of clarity when "with" is not included. Merriam Webster's editor, Peter Sokolowski, elaborates: http://www.learnersdictionary.com/qa/meet-and-meet-with
Nonsensical is a pretty accurate description here. Meeting someone implies that you've never met before, which is not possible with a former friend. Meeting with someone implies that you decided with the person (whether or not you've met before) to get together somewhere. If the meeting is simply a chance encounter with the former friend, then we would say something like "I ran into my old friend". In any case, one would never say "He is meeting an old friend".
In any case, "he is meeting an old friend" is not at all nonsensical and is very much common in English.
"What is Steve doing tonight?"
"He is meeting an old friend."
Of course, the "with" could be added, but meetings don't have to be chance encounters. Your assertion that that is an implication is obviously false (at least if you mean necessary, which is clear from your comment).
Wenn du nach Bedeutungen auf Deutsch fragen kannst, empfehle ich dir Duden ;)
- "old friend" - "alte(r) Freund(in)"
- "former friend" - "ehemalige(r) Freund(in)"
While I don't know what translation they used for the German dubbing of these movies, this doesn't seem like a very good translation (it certainly wouldn't be a very faithful one), and it would be quite weird to address someone as "ehemaliger Freund" anyway (and I'd suspect that addressing someone as "former friend" would be equally weird in English).
"He meets a former friend" is unnatural. To "meet someone" implies that is the first time. To "meet with someone" implies that you already know each other, which is clearly the case with a former friend. "He meets with a former friend" should be accepted. (It was not) "He meets a former friend" should not be accepted.