While want the others have said below is correct, I personally do think there is a grammatical distinction made in formal versus informal speech. For example, it is more formal and polite to ask: "Would you like something to drink?" versus: "Do you want something to drink?" or the even more brash "Want something to drink?" Grammatically there is a difference between the first two examples. This is similar to, for example in French, using the conditionnel to be more polite e.g. Je voudrais versus Je veux for I would like/ I want. Some English speakers (less so in the United States) will also do a similar reversal as is seen in French (e.g. Savez-vous is more polite than est-ce que vous savez...) where in English one could say "Have you any apples?"or more politely "Haven't you any apples?" (making the phrase negative allows the respondent to reply in the affirmative which is seen as a gesture of politness, this is also seen in Japanese). Both of these (Have you and Haven't you) are more polite than "Do you have..." My apologies for the long response. This is just a topic I have thought a lot about since many people assume English doesn't have differing levels of formality, I disagree. They aren't as concrete as in other languages but there is a way to be more formal beyond just avoiding slang :)

No, grammatical structure is the same. We speak more formally by being polite and avoiding slang. For example, "Good morning" or "Good afternoon" is more professional then "Hey" or "Hi".

English used to have formal address in the personal pronouns, namely, "Thee, thine, thou, thy," and so on. For example, "Madam, thine banquet is most exquisite!" [Madam, your banquet is most exquisite!] However, to know the correct usage of these old forms one needs to have studied Old English extensively, because the verbs change their ending, depending on the tense also. Another example: "Madam, thine banquet hast delighted mine appetite! I do thank thee for thy hospitality." [Madam, your banquet has delighted my appetite! I do thank you for your hospitality.] Notice, that the normal verb "has" carries the near-obsolete suffix -st, in this formal sentence. The best historical examples of formal English are most of the works of Shakespeare, and also the King James English translation of the Bible. These are worth studying if one is to understand the tense changes, and pronouns of formal Old English, since Old English retains the distinction between singular and plural in the 2nd and 3rd person pronouns! I hope this helps.

Yes, using "you" is historically formal...but English has no recognised formal...it's just when we form correct full sentances:)

English is different from German and French because do not have certain things that you only say in formal situations. As this other guy said, we speak more formally by not using slang.