Applying for a Schengen visa in another country than my main destination

In principle, no, as explained in earlier questions (e.g. Should my first trip be to the country which issued my Schengen Visa?) you should really apply to the country that will be your main destination and the German consulate shouldn't issue the visa without authorization from Belgium. However, if there is no Belgian consulate in your country, there are still two things you could do:

• Ask the relevant Belgian consulate if they have an agreement with another embassy/consulate in your country. One of the objectives of the Schengen agreement is to ensure that each Schengen member state is represented in all countries whose nationals require a visa. It does not mean that you can pick a consulate or that all consulates are allowed to issue visas for other countries but if one member state has no consulate in your country, there might be an agreement to channel applications through another member state's consulate. Benelux countries often have such agreements with each other (e.g. in Indonesia) so you might for example be able to apply to the nearest Dutch consulate (even if you don't go to the Netherlands at all). France also handles visas for Belgium in some countries (e.g. Congo-Brazzaville). The Foreign ministry publishes a table of all these agreements.
• Try nonetheless. The German consulate will most likely decline to process your application but then it should simply inform you and refund the fee (i.e. it's not treated as a negative decision). I wouldn't necessarily do it (it's just wasting time for all those involved) but at least nothing really bad should happen.

Details about all this can be found on pp. 19-23 of the Handbook for the processing of visa applications and the modification of issued visas