Hi Sami I did exactly the same thing you did :)
But it is creating problems later.
If you created extra form fields problem is bigger if not not a very big problem. But to have a normal functioning language system there is no other method for now besides creating the language module.
All the English to your language translation through polyglot is in sys_localisation_keys table. If you have custom fields they are registered to two more tables as you may see below.
The best solution is creating the language modul .
Check this:
....
During my Turkish Language module creation I had many problems 

* Before creating the module I did Turkish translations over English module from polygot. This was a wrong strategy from the beginning (and Baloo warned me for this :) )
* When I uninstall English module the the data lists like cities in Turkey (86) or Medical Faculties  (99) on forms module they all lost their titles they were like bx_pre..... something, even guessing what is what becomes almost impossible  .
I observed the database by creating custom form elements and checking where they are registered in database and cache from backup clone site my findings were:
They were recorded to sys_form_pre_lists and sys_form_pre_values

Restoring these to new database was not enough also it needed sys_localisation_keys table restoration. In this table each language has a language key value like English is 3 Turkish becomes 4
Also in cache there is an English language file. This has all the values but restoring this from backup is only creating a temporary full relief if the database is not correct.

After these table restorations now I can install uninstall restore recompile languages and my form titles are not being effected.