Being a native French speaker, I'm always looking for any hint of French language content and simply reading of hearing a French word in the middle of a Vocaloid song is enough to please me. Even if these are quite obvious for a native French speaker, these are so scarce they're hard to find. Nonetheless, some are more obvious than other.

French Version Here : Les bons et mauvais côtés de la recherche de contenu francophone dans la culture Vocaloid

Per example, I was delighted when I first heard of ALYS, a French digital singer that would sing in French as well as in Japanese that is under development. However, I did not expected that it would be so much different than Japanese ones nor its demo song would make it to the Top 20 on nicovideo. At that time, her official name wasn't known yet. It just something completely different from usual and people just liked that.

ALYS Demo Song - Avenir (Cover by the voice provider of ALYS) :

Some other references to the French language brought out some questions on how far could the French language be used by non natives and on how I use the Japanese as a second language. I heard many of those "off topic" use of words and grammar mistakes thought impossible by native speakers. These mistakes are probably a result of the complexity of the French language. On the other side, there are good example of use of the French language.

My personal favorite use of the language is from Mitchie M successful song "VIVA HAPPY!".

At around 0:50, it is said "愛せれば Que sera sera". It is a perfect use of the future simple verb tense which does not exists in Japanese. It was so great I could not believe it was French at first. Now I think about it, its probably because of the pronunciation which sounded like Italian or Spanish.

Two reasons can explain the lack of french content: the lack of knowledge of the language and the lack of singer able to sing in French. First, the French language is a language with a very complex grammar that is completely different from the Japanese language. This makes writing full sentences difficult for Japanese native. The main difference is extensive use of articles and gender differentiation for every nouns. Per example, a chair (une chaise) is a feminine noun while a desk (un bureau) is a masculine noun. Learning a new language is hard and requires a lot of time and the French language is even harder than average. That explains probably why french content is so scarce.

There's another reason to the scarce french content - so far, there is no french good Vocaloid, UTAU or CeVIO available. And the only promising one is still under development. ALYS as said before is a French digital singer. Originaly anounced as a Vocaloid it has been revealed that ALYS would be released for CeVIO with a Vocaloid release later. Vocalo-Ps can try to make a Japanese or English Vocaloid sing in French but results may be really decieving. Until then, there will not be a lot of french content.