If one could not speak French, one would say "Je ne peut pas parler francais", although a great idiom to use is "je parle francais comme une vache espagnol" (I speak French like a Spanish cow). Or you could say "Mon francais, c'est zero!"
I observe, though, that facility for language varies from person to person, that a
language is easier to learn the younger one starts, and that the proper *accent* is nearly impossible to learn once one is in the midst of puberty.
The last one may sound weird, but it's been proven. Our brains apparently start to change, and our instinctive pronunciations change. This may be particularly frustrating for French speakers! It also explains why some immigrants to the US speak English with an American accent, while others never quite lose their native accent, even within the same *family*.
I think it's pointless to argue which language is "easiest" to learn. Someone from China may find that English is difficult to get right, while an American may find Japanese particularly difficult to master. Why? Well, Chinese has much simpler rules for grammar, particularly tenses and declensions. Even for English, it's hard to get all the grammar to come out right all the time, if you're always translating in your head first.
For an American, the grammar and perhaps even the writing for Japanese is not impossible, but the usage is fraught with peril. I think that the Japanese language is more intimately bound up in the culture than almost any other language, and without knowing the culture one is bound to make a mistake. Because of the culture, that mistake will offend most people, or at least leave them with the conviction that you, like all Americans, are barbarians (in the classic definition of that word). With luck, you might have somewhat close Japanese friends who will giggle in embarrassment, but they probably won't correct you, even if you ask.
A final note: If you go to France, learn a bit of French even if you pronounce it like a Spanish cow. Then use it. The French always love those who appreciate them enough to *try* to speak French. If you get back a blizzard of words, just say "Pardonnez-moi?"
