Don't choose just anybody to correct your text in English!
I have a friend who once volunteered to take over an English proofreading job that
I had begun while I was studying as I did not have the time to finish it
not a particularly technical text.
Unfortunately, shortly afterwards, my friend told me that he was having serious
trouble understanding the text, and therefore making the necessary corrections. He, too,
was a highly qualified native speaker of English (with a university degree in the field in
question geology), but with one slight difference: he only spoke German,
Now, since the author of the text was an Italian native speaker (thinking in
Italian and writing down words in English), there were quite a few places in the text
where one had to be fluent in Italian in order to be able to perform the reverse mental
process of translating back into Italian (unscrambling the "Italian" English)
and then into proper English as a result of the distinctly Italian
structure of the sentences and the choice of incorrect words in English.
This real-life example shows just how important it is to choose the right
person for your proofreading job: someone capable of grasping the exact
meaning as intended by the author, picking up on any inconsistencies
or unintended ambiguities, correcting any grammatical
and lexical mistakes, improving the style and giving
your text the professional linguistic attention that it deserves, bearing in mind the target
audience (English native speakers, non-native speakers etc.) at all times.
My foreign languages are German, Italian and French.