grammar - Usage of commas in Japanese sentences

This might sound like a strange question, but how does the usage of commas differ when used in Japanese compared to English?

I believe りんご、オレンジとバナナ wouldn't work, but that it's OK to list like りんご、オレンジ、バナナ or りんご、オレンジ、またはバナナ. When should りんごとオレンジとバナナ and similar be used instead of commas or vice-versa?

I've heard that going e.g. 分かりにくくて、読みたくない with i-adjectives isn't correct but 分かりにくいし、読みたくない and 分かりにくく、読みたくない is. I'm guessing it's OK to go 簡単で、特に問題はない and 簡単し、特に問題はない right?

Additionally, what is the meaning of 、。 at the end of a sentence, e.g.　気にしてなかったけど、。? I think it might have some kind of emotive effect, so I think I'd translate it as "I didn't really care though" (for emphasis.) I might translate 、。 as "I'm flustered that..." in some other contexts but I'm not sure.

Answer

The symbol “、” is called [読点]{とうてん}. It is used to denote a semantic separation or a pause. Compared to comma in English, the usage of 読点 in Japanese is less governed by the grammatical rules. In other words, in Japanese, the author is free to use or not to use 読点 in any place where a separation makes sense.

When two nouns are placed side by side without any particle, a 読点 is almost necessary.

I believe りんご、オレンジとバナナ wouldn't work, but that it's OK to list like りんご、オレンジ、バナナ or りんご、オレンジ、またはバナナ. When should りんごとオレンジとバナナ and similar be used instead of commas or vice-versa?

You are required to put a 読点 between two nouns placed side by side. You are free to put 読点 after particle と or before adverb または.

I've heard that going e.g. 分かりにくくて、読みたくない with i-adjectives isn't correct but 分かりにくいし、読みたくない and 分かりにくく、読みたくない is. I'm guessing it's OK to go 簡単で、特に問題はない and 簡単し、特に問題はない right?

There is no verb 簡単する, and therefore 簡単し is ungrammatical. Maybe you meant “簡単だし、特に問題はない.”

All of “分かりにくくて、読みたくない,” “分かりにくいし、読みたくない,” “分かりにくく、読みたくない,” “簡単で、特に問題はない,” and “簡単だし、特に問題はない” are grammatical. In these examples, you can also omit the 読点. However, depending on the rest of the sentence, omitting the 読点 in “簡単で、特に問題はない” or “簡単だし、特に問題はない” may make the sentence harder to read because it connects two descriptions (簡単だ and 特に問題はない) of different length.

Additionally, what is the meaning of 、。 at the end of a sentence, e.g.　気にしてなかったけど、。?

The combination “、。” is incorrect in the standard orthography in Japanese. Some people make a nonstandard use of three 読点 (、、、) in place of 三点リーダー (…), which is used in the same way as the ellipsis in English. I would interpret “、。” as “…。” if anyone uses the former.