By the way, although everybody would understand what you meant by "thorn in my foot," the usual expression in English is "a thorn in my side."

If I may make a suggestion? Have you tried concentrating entirely on one aspect of English grammar at a time? Instead of trying to get everything right all at once - to become perfect at the 'drop of a hat,' as we say in English, it may be worth trying to practice learning one thing at once.. Try to become perfect at one thing at a time.. ... As you are French, my suggestion is that the place that you should start is with plurals. I have noticed that French people repeatedly tend to miss off the "s," from our plural words - as you have with "friends," in your text. I believe that the reason that this happens is probably because, in French, it is only the sound of the article that tends to change when you say words in the plural i.e Les Pommes instead of La Pomme... you guys change the spelling but not the pronunciation of the noun in the plural. It may be worth thinking about how the French language works and then thinking about how the English language works and then repeatedly practicing elements - such as that one - where there is an obvious difference between the two languages.