I got it done by using, BMfont. : https://www.angelcode.com/products/bmfont/
[https://ttf2fnt.com by @Milos_Bejda is a very simple solution. With a few easy steps we can convert any ttf files into fnt. And if your application needs a-z, A-Z, numbers and basic special characters its the place for you. It will generate a mapping file and a png image with the above mentioned characters.]
If you are in need of more special characters [é,®,û, ï, ü : like @Alextoul has asked] we need to go with a sophisticated tool like bmfont which will enable us to choose all the characters we want.
Once downloaded: you open it: the home screen of bmfont
The 1st step is to load the font you want in 'Font Settings' . font selection is done here
And now in 'Export Options' make required changes. font size can be set here. And for normal black characters set the ARGB as A: glyph, R: zero, G: zero, B: zero. (refer image)
Once done you can see the all the character sets as a list in the homepage. Select the sets you need. select the character sets.
Now in the options 'Save bitmap font as' or hit ctrl+s.
If you have done it right, you will get a fnt file along with all the character sets in a set of png files.
