Multilanguage support

[jnehring]

Currently the pipeline supports one language only. The first version will support German only. To make it multilingual we could

• We could make the language a parameter of the file upload.
• We could include the language detection endpoint.

Currently I focus on the monolingual pipeline and this issue is just a reminder to do it later.

[jnehring]

this will be implemented by #15. the user has to specify the pipeline and the pipeline specifies the processing language.