Confusing

Inappropriate but understandable

Suggestions and uncertain changes

我有另外一个翻译练习！我很感谢你们的帮助。（Please don't translate. Translation requires more skills and experience than speaking a language fluently. What makes sense in English might be nonsense if literally translated into Chinese.)

If it is not convenient to talk to Professor Li now, I can come back again this afternoon -- 如果现在跟李教授讨论不太方便的话，我可以这个下午回来。
On what date does the Beijing University start its summer vacation? -- 北京大学几月几日开始放暑假？ （Again, you are trying to translate something literally into Chinese.几月几号 is not wrong, but it's not strict standard written Chinese. In Shanghainese, we also say 几月几号. But since we are talking about standard written Chinese, which follows the grammatical rules and shares vocabulary with Mandarin, you'd better say 几月几日)
How many countries are there in Asia? -- 亚洲有多少个国家？
In which hotel are you staying? -- 你呆在哪家旅馆？
I like eating spicy things, such as tofu with hot peppery sauce, hot peppery chicken with peanuts, etc -- 我喜欢吃辣的，比如麻婆豆腐，宫保鸡丁 (??)，等等。 (All is good)
If you don’t want to go to Taiwan in your winter vacation, you can go next year -- 如果不想在寒假时去台湾的话，你就可以明年去。
How many overseas students are there in your class? -- 你的班里有几个留学生？
His visa was dealt with very quickly -- 他的签证处理得很快。
I’m not too accustomed to eating Sichuan cuisine -- 我不太习惯吃四川菜。
I don’t really comprehend his meaning -- 他的意思我不太理解。

我有另外一个翻译练习！我很赞赏你们的帮助。

If it is not convenient to talk to Professor Li now, I can come back again this afternoon -- 如果现在跟李教授这时讨论不太方便的话，我就这个下午再会[回]来。
On what date [I guess, your English suffers when you immerse in Chinese too much.  This happens to me too!] When does the Beijing University start its summer vacation? -- 北京大学几月几时号开始暑假？
How many countries are there in Asia? -- 亚洲有几多少个国家？
In which hotel are you staying? -- 你呆在哪 一家旅馆住？ Unless you are speaking to a very dear friend, this can be construed as impolite.
I like eating spicy things, such as tofu with hot peppery sauce, hot peppery chicken with peanuts, etc -- 我喜欢吃辣的，比如麻婆豆腐，宫保鸡丁[Correct, also 公 may be used also.]  (??)，等等。
If you don’t want to go to Taiwan in your winter vacation, you can go next year -- 如果不想在寒假时去台湾的话，你就可以明年去。
How many overseas students are there in your class? -- 你的班里有几个留学生？
His visa was dealt with very quickly -- 他的签/通行/证处理得很快。
I’m not too accustomed to eating Sichuan cuisine -- 我不太习惯吃四川菜。
I don’t really comprehend his meaning -- 他的意思我不太理解他的意思。

我有另外一个翻译练习！我很赞赏你们的帮助。

If it is not convenient to talk to Professor Li now, I can come back again this afternoon -- 如果现在跟李教授讨论不太方便的话，我可以(can)今天下午再回来。

[We usually say "今天下午", literally meaning "the afternoon of today", to convey the idea of "this afternoon".] 
On what date does the Beijing University start its summer vacation? -- 北京大学几月几号开始放暑假？
How many countries are there in Asia? -- 亚洲有多少个国家？
In which hotel are you staying? -- 你住在哪家旅馆？
I like eating spicy things, such as tofu with hot peppery sauce, hot peppery chicken with peanuts, etc -- 我喜欢吃辣的，比如麻婆豆腐，宫保鸡丁 (??)，等等。
If you don’t want to go to Taiwan in your winter vacation, you can go next year -- 如果你不想在寒假时去台湾的话，你就可以明年去。
How many overseas students are there in your class? -- 你的班里有几个留学生？
His visa was dealt with very quickly -- 他的签证处理得很快／他的签证很快就弄妥了。
I’m not too accustomed to eating Sichuan cuisine -- 我不太习惯吃四川菜。
I don’t really comprehend his meaning -- 我不太理解他的意思。

我有另外一个翻译练习！我很赞赏你们的帮助。

If it is not convenient to talk to Professor Li now, I can come back again this afternoon -- 如果现在跟李教授讨论不太方便的话，我就这个下午会回来。 我这个下午就能回来。
On what date does the Beijing University start its summer vacation? -- 北京大学几月几号开始暑假？
How many countries are there in Asia? -- 亚洲有多少个国家？
In which hotel are you staying? -- 你呆在哪家旅馆？
I like eating spicy things, such as tofu with hot peppery sauce, hot peppery chicken with peanuts, etc -- 我喜欢吃辣的，比如麻婆豆腐，宫保鸡丁 (??)，等等。
If you don’t want to go to Taiwan in your winter vacation, you can go next year -- 如果不想在寒假时去台湾的话，你就可以明年去。 你可以明年去。
How many overseas students are there in your class? -- 你的班里有几个留学生？
His visa was dealt with very quickly -- 他的签证处理得很快。
I’m not too accustomed to eating Sichuan cuisine -- 我不太习惯吃四川菜。
I don’t really comprehend his meaning -- 他的意思我不太理解。

总的来说，翻译的挺好。well done！

我有另外一个翻译练习！我很感谢你们的帮助。

If it is not convenient to talk to Professor Li now, I can come back again this afternoon -- 如果现在李教授不太方便的话，我下午再来。
On what date does the Beijing University start its summer vacation? -- 北京大学放暑假从几月几号开始？
How many countries are there in Asia? -- 亚洲有多少个国家？
In which hotel are you staying? -- 你住在哪家旅馆？   呆，一般是用于长时间在某一个地方。
I like eating spicy things, such as tofu with hot peppery sauce, hot peppery chicken with peanuts, etc -- 我喜欢吃辣的，比如麻婆豆腐，宫保鸡丁,等等。
If you don’t want to go to Taiwan in your winter vacation, you can go next year -- 如果放寒假的时候，你不想去台湾，你可以明年去。
How many overseas students are there in your class? -- 你的班里有几个留学生？
His visa was dealt with very quickly -- 他的签证处理，办得很快。
I’m not too accustomed to eating Sichuan cuisine -- 我不太习惯吃四川菜。
I don’t really comprehend his meaning -- 他的意思我不太懂。