A lot of language is related to the way different cultures think. To be truly multilingual a person must be able to think in different ways.
This was the first sentence of a writing sample created recently by an applicant for a position as a senior editor:
I showed this to our last senior editor, Shreedhar, and he explained to me that "then nothing can be both useful and adorning like a pergola" is a literal translation of the way the phrase would be constructed in Tamil. A native English speaker would not construct a phrase like that.If you are looking forward to decorate your backyard, then nothing can be both useful and adorning like a pergola.
This person understood English the language, but not English way of thinking. On the other hand, you could talk to Shreedhar or Memenode online for years without ever realizing that they were not actually native English speakers.
For a look at some examples of how English and Indian English differ, read through Wikipedia: Indian English.