"I met Ainu people."
When you meet someone unintentionally or without having organised it per se ~に会う is used, because the action of meeting is being performed 'toward' that person. If you are "meeting with" someone, which gives the impression you are meeting each other (and you both know about it) you use と会う。
スーパーで田中さんに会いました。I met Tanaka san in the supermarket (and it was unexpected).
きのうカフェで友達と会いました。Yesterday I met with a friend in a cafe (and we both knew about it and had planned it a few days before).
This is the general nuance in any case.
Just in case anyone is learning the wrong way to say アイヌの人, it should be pronounced "ainu no hito," not "ainu no jin." For the translation exercise, it gives the correct pronunciation, but when you're trying to piece together the sentence yourself, it comes up as "jin" when you select 人.
Pardon, but i am also interested in what the difference is between ainujin and ainunojin but my Japanese isn't quite this good and the mobile app doesn't allow copying comments to translate. Update: at my computer now. Are you saying that --jin is used for nationalities and --nojin is used for ethnicities?
It doesn’t seem that confusing to me: When talking about nationality/ethnicity, read ひと when there is a の before it, otherwise read じん. Of course you do still need to know when you have to add の, but even so it’s still a lot more consistent than English (sometimes -an, sometimes -ian, sometimes -ish, in a few cases -i (e.g. Pakistani), sometimes you have to replace a syllable in of the country name (Sweden => Swedish) or just straight up delete it (Germany => German). And that’s not even counting cases which are just completely irregular (e.g. France => French)).
The suffix -たち is normally reserved for two cases:
- definite plurals: ”the Ainu people” (as opposed to just “[some] Ainu people”)
- when addressing a group: 子供たち、あれを食べてはいけませんよ。 “Children, you mustn’t eat that.”
Other than that, the plural normally goes unmarked. Usually singular or plural can either inferred to from context or it is unimportant to begin with. In the example sentence for instance, it probably doesn’t matter if the speaker met one or several Ainu people. Most likely the important thing is the new experience.