When you make your suggestion, Cordelia gives you a blank look.
"Let me get this straight," she says slowly. "You can use magic to make it easier to learn other languages."
"Yes." You don't bother explaining that it works by a combination of Augmenting the language centers of the brain, Summoning the concept of "Japanese language" from the collective unconscious, and Divining the concept to copy/paste it into your memories. Past experience has taught you that Cordelia does not particularly care about the details of magic, as long as it works and the results aren't gross.
"And you want to learn Japanese before we arrive in Japan," Cordelia continues.
"...yes?" You have the feeling that she's leading up to a conclusion you aren't going to like.
"So tell me, then; why didn't you start studying Japanese like, a week ago, when you first found out you were going on this trip?"
Ah. Now that you think on it, yes, that probably would have been a good idea.
Cordelia sees the chagrined realization dawning in your expression, and sighs. "Honestly, Alex, you can be a really dumb smart person sometimes, you know that? Now, come on. Unlike some people, I actually cracked a few books on this subject. Maybe it'll help."
You spend the next several hours practicing. Your magic isn't yet at the level where you can permanently copy a working understanding of something as complex as an entire language into someone's mind; the spell you're using is just a training aid, meant to accelerate the normal learning process. If it takes a child six years to get a solid foundation in language, and an adult with access to teachers and a well-explained lexicon six months to achieve the same, someone using this spell could reduce their learning time from years to months, or from months to weeks. With these few hours, the magic is able to refine the bits and pieces you've picked up from Lu-sensei over the years and what Cordelia retains from her week of self-study into a bare-bones level of comprehension. You'll probably come across sounding like two year olds with a learning disability, but you can manage the basic phrases - "Hello, my name is Alex," "I apologize," "which way to the bathroom?" and "bah wheep grah nah wheep ninnybong," that sort of thing - and your comprehension will continue to improve as you spend more time in the company of and talking with native speakers. The flip side is that the language will fade relatively quickly if you don't keep renewing the learning spell and practicing on a daily basis, at least until you have "mastered" basic Japanese.
Gained Japanese F-
Briar listens in on your lesson for maybe ten minutes, growing increasingly bored. One of the little perks she gets from being a fairy is general comprehension of most spoken languages, which makes lessons like this rather pointless, in addition to dull.
"I'm going to go explore a bit more," she says. "The plane leaves tomorrow at eight, right?" When you nod, she does so in kind. "Right, then I'll be back by six. Have fun, Alex." And with that, she zips out the open balcony door, flying past Cordelia's head in the process. The brunette blinks.
"What was that?"
"Just my invisible fairy companion getting bored and going looking for something interesting," you say with total honesty. "Voice, or wings?"
"Definitely wings," Cordy replies, looking around suspiciously. "Like the world's biggest butterfly deciding at the last second not to land in my hair."
"You're getting closer to seeing her, Cordy," you congratulate her.
"Yeah, well... I don't suppose there are spells that would speed that up, too?"
"I know several. All are temporary, and most would make you start seeing other invisible things besides Briar - and the overwhelming majority of those are nowhere near as cute or friendly as she is. Want to give one a try anyway?"
"Pass."
Since your flight leaves fairly early the next day, you and Cordelia agree to call it an early night, and you use a simple sleep spell to make sure you both nod off despite not being all that tired. The mild resistance to magic you gain by dint of having any sorcerous talent at all eventually shrugs off the effect, and you wake up at just shy of twelve in the morning. Lu-sensei is doing his sawmill impression, and a quick magical scan of Cordelia's room informs you that she is still out like a light, and will probably remain so until sunrise.
It's midnight on a warm spring evening in Hawaii. You're alone, you're armed with magic and mystical kung fu, and you've got nowhere to be for the next six hours.