Applying for Belgian nationality

If you have been working for all 7 years, then you will go for the "declaration" of nationality process. You will get a paper from your payroll company explaining what social security you've paid, and that proves both your social and economic integration, so no further language requirements.

I'd suggest you get a Dutch speaker to help you at the commune. Some will deal with you quite happily in English and sometimes French as well. Some will only do Dutch.

Some (at least) Flemish communes have been refused to accept social and economic integration on the basis of employment where that employment uses a non-Belgian language (ie English). If your employment environment is francophone that shouldn't present any problems.
Unless you are in receipt of a pension or are too handicapped to work, it is an absolute requirement of the law on the acquisition of nationality that you can demonstrate knowledge of one of the three languages to A2 standard, the "working" qualification merely short-cuts the need for certification.

I believe that you will need to demonstrate 5 years of unbroken social security payments. I had a 2 week gap between being an employee and a an independent, so I had to take the 10 year option.
A gap in the validity of your ID card (say you were late renewing it by a couple of weeks) can also cause a problem.
5 year option does not need proof of language but with your Flanders situation it might be worth going to Forem in Nivelles and taking the French test (A2 needed). It is free and takes an hour or so. This would prove that you have one of the national languages. A Dutch commune will not want to talk French with you to prove it is an adequate level.
Taking a Flemish speaking friend would be a good back up. Start by seeing if they will do it in English (ask in Flemish) and only use friend if not, on the basis that your Flemish is not fluent enough. It's called 'playing the game'.

I was in a similar situation and had some doubts, so I decided to go to the organisation Objectif (www.allrights.be). They provide you with clear guidance based on your particular situation and even advise what is needed for what commune and what to say, they even provide you with template letters if needed. And it is all for free. I think it is worth checking with them before going to the commune. It helped me to avoid some frustrations.
Having their help, I was able to apply to citizenship without any problems and delays from the first attempt.
Good luck,
D

As far as I know you only need to know 'one of the national languages' to apply for citizenship, regardless of where you live. That does beg the question...why did you move to Flanders if you don't speak a word of Dutch?

Don’t forget to get 3 or 4 letters in local languages to say you will be a good citizen! Best are friends, colleagues, boss, doctor. Just short saying they support your applications and with copy of their ID card to prove they are genuine.

About translation of documents: from my experience in Brussels it should not be a problem as it is bilingual and part of my documents were in Dutch and part in French, while in Flamish part it might be a different story. You better check with Objektif, and specify which commune in Flanders it is.

I would assume you write about birth certificate. If so, you can check on-line if you indeed need legalisation and apostle on this web-site: http://diplomatie.belgium.be/fr/Services/Legalisation_de_documents/Crite... . This was also suggested by Objektif and in my case it worked very well: I avoided loss of time and money on legalisation as in my case legalisation and apostille were not needed. I learned from this web-site that my country of birth issues documents that do not need legalisation in BE according to Vienna Convention 1976 and, thus, I ordered specific document recognised by Belgian authorities without apostille.

D.