'Under the table' odd jobs?

This kind of informal job does happen, but is illegal. As a foreigner (who can be deported when found to have done something illegal) it is a high risk and I would recommend not to do it.
He should better get a proper work permit and find a job that is legal, pay tax and social security.

Without language abilities, not only will he have problems finding any job, but he will also face big problems in daily life. I suggest him to attend a full-time language class for the first few months until comfortable in German. Such classes are available at Volkshochschule, universities and some other organisations.

Hello!

Thanks for the reply, it's obviously extremely important that I know it's considered illegal, now!

It really is such a shame to have had a fluent German speaking father who was never willing to teach him, otherwise
we'd be in such a different situation in the upcoming months!

I have suggested to him that he enroll in language courses, as well.

Have you heard of any opportunities for French speakers, though?

Hi Sophie-Anne,

You wrote a rather long introduction and it is good to see someone still has the brains enough to want to find out what is going on in the country they plan to live and work in for a while.  Here is my advice:  learn the language or at least the basics of a working knowledge of it before going there; if you want to work, then you have to have an education or skill that is "marketable"; since you come from another country as Germany, then you may find it easier to a find a job in Germany related to your education/skill and the country you come from and you will need to find an employer who will want to sponsor you for your work permit.  It is best to have aacademic degree and speak/read/write German if you are going to move to Germany. One word to the wise: If you are going to use your academic degree from a foreign country, then you need to have it officially recognized once you get to Germany so get an official transcript of your degree if possible with a seal of some kind but only show it and give a copy to the certifying agency; using a degree not recognized (each person must have their degree individually recognized) is fraud that is punishable by one year in prison or a fine in Germany; and we did have a fraud case like that at work and the woman went to jail for it.  By way, Heidelberg is not that close to France (depending, of course, on how you define "close");  just take a look at a map. I had some co-workers in Switzerland years ago and in meetings I always had to ask them to speak in high-German slowly because "everyday" Swiss-German is not that easy to understand.  good luck with your job search, Mac