There is a non english international technical community debating interesting things in a non flame war style?

In what language do they communicate? Esperanto?

(I suppose some want french to be lingua franca, others spanish, others chinese .. but de facto those ain't international spoken languages, despite having lots of speakers)

No, I speak three languages fluently, and there is no $LANGUAGE non-US resource/community that has discussions on the same level as HN, particularly then it comes to the width of experience of the users + (sometimes) nuance when the topic is bit divisive.