Is it reasonable to use language codes? Yes. Probably. They're fairly recognizable. Is it better to use the full names...? "Better" is contextual.
It's good of you to mentioned that the context is technical documentation, and since that's the case I would posit that, while the full names may be prettier and slightly more informative, they are not necessarily "better".
Language codes will be recognizable as such in even moderately technical material, a users' manual for instance, and the actual meaning of the codes should be recognizable to the speakers of that language. And if you have any fear that they will be received with any uncertainty you may include the full names (in the native language--not using the English equivalent as in the example from the original question) as a smaller sub-heading or on hover, or some such device, depending on the capabilities of your medium.
Another advantage is that language codes will scan faster than the full names. They can be used almost as an icon would, allowing near-instant recognition of a basic significance, and don't need to convey much meaning of their own.
They're easier to keep out of the way, as they are so concise, which is a plus as once one has found the language he is looking for he doesn't need them anymore.
Finally, in some contexts, it is possible that they are less ambiguous than full names--there are 3 Norwegians as I understand--as they are a standard and thus designed to exact.
The only caveat that I might include is that depending on the perceived literacy of the audience you may need to consider languages which to not use a Romanesque alphabet, but again, you're asking about technical documentation, so likely the user has been well exposed to our characters.