When should I use 文 and 国?

韩国书店, "Korean bookstore" (from Korea), When the store sells Korean products (not just books).

韩文书店, "Korean-language bookstore", When the store specializes in books written in Korean.

韩文书店means书店 only sells books written in Korean language; 韩国书店means书店located in Korean;文means language, 国 means country。但是有一个特殊例子，就是国与文连用，“国文”特指汉语。

韩文means the Korean language, 韩国 means the country. If it's about 书店，in most cases they mean the same. I heard phrase like "韩国超市chāo shì”，in this case you can't use 韩文。

the character 文 means language and character in Chinese, but 国 means country, so these words like: 韩文、中文、日文 all means the characters or languages of different countries.
however 中国菜、中国人、中国书店 or other phrases contain 国 are related to countries, not language or characters. so it's not allowed to say 中文菜、中文人
书店 is maybe related to language and character, but we say *国书店 more often. so it's more safe to say *国书店
( and in China, we seldome see a bookstore which just sells Korean books)