I've been developing a new, fresh website called FileChange.net (awesome file conversation tool).
I have created this website multi-lingual, each language in different sub-domain.
For example:
FileChange - Kostenloser Online Dateityp Konverter - German Version
FileChange - Free Online File Converter (Spanish) - Spanish Version
File Converter Hebrew Version - Hebrew Version
And ofcourse the English International version, FileChange - Free Online File Converter.

I have some past experience in SEO and link building I've been doing this only for specific country and target, and now I want to try something international with more languages.

I need your help with link developement on this project, How I should do this smart and effective?

Thanks in advance! (I know I got alot of work to do)