Débats à propos du terme à employer
frwikipedia can still keep its choice; technically, all they have to do is to apply their prefered form in their local "MediaWiki namespace and block it to be overriden by bot imports. For me this decision is purely local to frwiki, and I should have not been blamed on frwiki for applying a correct translation. If frwiki want to have their prefered translation given, they should indicate it in the "/qqq" doc page with a link to their decision (actually never done by a real procedure but decided by very few admin users in an informal talk page archived rapidly and impossible to find later. They complain this was discussed multiple times, but the change to "citer" was made multiple times by users that were never able to locate their decision or discuss it seriously (these discussions have a very short lifetime: 1 day only, and hidden within a mass of messages for any topics in frwikipedia). It's up to frwikipedia to create their own translation support tracking page, and keep a record of their past decision (which are not necessarily the best as there are other options they never thought about). Such tracking is up to those admins to do so they will track when changes will be needed (because they will lock their current choice and will not allow any new value being imported from translatewiki.net).
The "false friend" is in fact a false argument. "source" is as much ambiguous as "cite" if they are used alone, the real meaning is when associating both: for English and all other languages, "cite" is considered enough, but a few frwikipedia admins think that "source" alone is enough. We have various places where "source" would be ambiguous (look at the discussion about how "wikitext" or "source" are used and translated with different meanings, including source of information, source language of translation, source document, source author... the context of use is not clear; even for the use of the label in templates which are used by tempaltes like Template:Cite and tools like Citoid, both being named in French using "cite" and not "source").
It's very unfortunate because all other languages have not made this decision (including for other regional languages of France, and the only opinions were those expressed by frwikipedia admins in France, that actually don't participate a lot to translations and do not care about consistency, even in frwikipedia itself, or don't take the time to signal to translators that they have another opinion). They blamed me publicly in their "Bistro", but even forgot to contact me to signal they disagreed with it (and it was impossible for me to know that there was some earlier separate discussion visible only one day in the Bristro since several years, and not even conducted in an appropriate project page. I consider such public blame (with ad nominem attacks) very unfriendly and in fact opposed to normal rules of cooperation. And not all French tralators use French Wikipedia (they may work on other wikis and rarely visit the French Wikipedia to follow its "Bistro" full of uncategorized junks, and actually meant only to provide instant help to users but not support of the community at large and the long term).
We should include on this wiki a template we can use in "/qqq" to display specific translation guides for specific wikis in specific languages, and at least for specific languages even if the "/qqq" page is written mostly in English. But I've not found any way to have the "/qqq" subpages detect the target language used in the translation tool, so that such template would work. Now If we don't use such template, all translators in all languages will see comments relevant only to a specific wiki. If all wikis want to include their own notices, the "/qqq" pages will be hard to read and manage, too long and the notice will not even be displayed in the translation tool without forcing all users to scroll down the text to see that there are specific notices for specific wikis or languages.
And anyway translatewiki.net is not just for Wikipedia or Wikimedia; there are lot of other wikis using MediaWiki outside Wikimedia, and that still want to use the same base translations by default without being bound in their own sites (including commons, frwikisource, metawiki, and community wikis for specific regions) to the very specific frwikipedia rules imposed only by a few frwikipedia admins that have no privilege at all on other wikis.
Yes, a lot of wikis are using MediaWiki and frwiki is the biggest french speaking wiki : I think the community is in the best position to judge the translation and why it corresponds better. You can criticize the approach, but to this day, it's the most developed consensus. If you don't like the approach, you can start an interwiki survey and ask all contributors for their opinion of this translation. Personally, I don't have the time and energy to organize such a process.
No one insulted you, don't take this dispute for a personal matter: you proposed a translation and some contributors didn't agree... It happens. I initiated the discussion and notified you in the original message: if it didn't work, it's not my fault.
I don't understand the "/qqq" stuff, or rather how it's supposed to solve the disagreement. I would also like to point out that not only the administrators have commented on this question. Also, the frwiki rules don't define this translation: it's the usage that prevails. Finally, the word "source" is no longer used, but the verb "sourcer" is, since a verb is used in English.