Is doing a Habilitation a financially viable decision? I know that a PhD is necessary to enter academia which means you can find a better job and get salary. 

But, how about doing a Habilitation in Germany? Does it have any positive impact on the career or financial situation as an international student?

For instance, say someone is barely employed. So, he is supposed to get an "actual" job after the completion of his PhD. But, can he postpone getting the job until he completes his Habilitation? What would be the financial implication?
You have to distinguish things here:


A Habilitation is a qualification level (not quite like an academic
degree but you can think that it is sort of a grand PhD with additional teaching). This does not mean
that you have to be employed but in most cases you will be because
otherwise it is going to be a bit difficult to finance your life for the time it takes (normally 4-8 years)
A Habilitation used to be the formal qualification level to become
Associate Professor and Full Professor. The position of an Assistant
Professor (German "Universitätsassistent") was usually the time when you worked on obtaining the
Habilitation. Today most job advertisements do not ask for a
Habiliation anymore. Instead it states something like "Habilitation 
or equivalent qualification". This allows hiring of international professors.
In daily university life a Habilitation might still be of
significant advantage. You (sadly) still hear phrases like "This guys does not even have a Habilitation - what does he even want". Also nobody will questions your ability to supervise students if you have the Habilitation (you can also without but it definitly still helps)
In non-academic jobs as in industry you will certainly not need a
Habilitation. It might rather be a disadvantage as you will be seen
as overqualified.