I think it’s kind of similar here. Some schools teach a second language in years 1 and/or 2 of primary/elementary school. This language is usually based on the demographic of the area, so for example, mine taught Italian 
and Chinese 
.
Then the rest depends on the high school (years 7-12, or ages 13-18, as you said).
At the end of primary school, there’s a big test to see what kind of high school you can get into. I managed to get into one of these “selective” schools, so in year 7, spending each term on a different language was compulsory. Ours were:
- Latin
- German
- French
- Japanese
After that, one year of a language is compulsory, so I took Japanese. I had a bit of a head start, knowing some kanji 
from having learnt some Chinese when I was younger, as kanji is the term for their mostly Chinese characters. (They do modify some a little so that they’re different. For example, ice 
in Chinese versus Japanese are 冰 and 氷, respectively.)
From then on, we could choose to pick up a language and either take that all the way through to year 12 or not. In years 9 and 10, I didn’t take any language, then I did Japanese in years 11 and 12. It took some catch-up with the Japanese, but I managed to do pretty well in my end of high school exams, so it worked out. 
Then, when I went to university, I took Chinese as a minor with my degree, while I majored in International Business which had a few classes on cross-cultural management.
It can be. (I understand the struggle with ADHD well, unfortunately.) But two things can help you a lot!
One: Use the language whenever you can. 
This is the obvious advice that anyone will tell you. But it really matters. If you don’t have anyone to speak to in the language, read books 
, magazines, poems, or even Wikipedia articles, watch movies 
and shows, and listen to music 
in the language. Immerse yourself as much as you can.
When you have time, even go out of your way to translate things! I used to translate Japanese and Chinese songs all the time to share with others when I was younger. This really helped me catch up in Japanese when I missed two years of it.
Two: 
Stop translating into your native language when you want to use the language. 
This is the weirder piece of advice, but I promise you, it will make you a much more natural language learner!
Instead, learn as a toddler learning their very first language learns! 
What this means is no more learning like, “Okay, so mačka/neko/māo/chat/katze is a “cat.”” 
Imagine a mental image of the cat and tie the word to that image. When you wish to learn the word for soup, image a soup 
. For car, imagine a car 
, and so on.
But how does this work for things that aren’t nouns? When you learn how to say “thank you,” tie the word to the feeling of gratitude you have for another. 
When you learn how to say you will go somewhere, imagine the act of going there. 
When you want to learn the word for “love,” 
“happy,” or “sad,” 
imagine that feeling. Don’t tie it to your native word, or you will forever be a translator, having the more difficult job of taking two steps to think of a word instead of one.
→ cat → māo
→ māo
It sounds crazy, but it works. And it’s not an easy mentality to get into at first, but it will make learning any language so much more natural. And you might even be able to think in the language twice as fast than you would have otherwise. 
Anyway, sorry for the rant you didn’t ask for. 
I was living my dream career of being a teacher for a moment. 
Thank you. You are right. I should be proud of all the things I’ve poured my heart into. I appreciate you pointing this out to me.
but when I have time, this is definitely how I will approach it! Thank you, so much!
You deserve it!
Oh, katakana words were my lifeline during my first time in Japan, with the most important of them all being カラオケ (karaoke) 
), but I think you would be an amazing teacher if you ever chose to pursue that path! Would you want to teach languages in general, or perhaps one (or more) specific languages?
In my eyes, the value really can’t be understated 