As a general rule, 不 appears before the word it negates. Therefore, the word order of a negative sentence affects its meaning.
我爸爸妈妈都不是老师。
Wǒ bà bà mā mā dōu bú shì lǎo shī 。
Neither of my parents are teachers.
Compare:
我爸爸妈妈不都是老师。
Wǒ bà bà mā mā bú dōu shì lǎo shī 。
My parents are not both teachers. (One is; the other isn’t.)
你身体不好，不可以喝酒。
Nǐ shēn tǐ bú hǎo ，bú kě yǐ hē jiǔ。
Your health is not good; you cannot drink (= you are not allowed to drink).
Compare:
你酒量不好，可以不喝酒。
Nǐ jiǔ liàng bú hǎo ，kě yǐ bú hē jiǔ 。
You get drunk easily; you don’t have to drink (= it’s OK if you don’t drink).
我的法文老师是日本人，他的法文不太好。
Wǒ de fǎ wén lǎo shī shì rì běn rén ，tā de fǎ wén bú tài hǎo 。
My French teacher is Japanese; his French is not very good (literally: not too good).
Compare:
我的英文老师是中国人，他的英文很不好。
Wǒ de yīng wén lǎo shī shì zhōng guó rén ，tā de yīng wén hěn bú hǎo 。
My English teacher is Chinese; his English is very bad.
[1] Yip, P. C., Rimmington, D., Xiaoming, Z., & Henson, R. (2009). Basic Chinese: a grammar and workbook. Taylor & Francis.
[2] Teng, W. H. (2016). Yufa! A practical guide to Mandarin Chinese grammar. Taylor & Francis.
