[android] How to keep the spaces at the end and/or at the beginning of a String?

I've no idea about Android in particular, but this looks like the usual XML whitespace handling - leading and trailing whitespace within an element is generally considered insignificant and removed. Try xml:space:

<string name="Toast_Memory_GameWon_part1" xml:space="preserve">you found ALL PAIRS ! on </string>
<string name="Toast_Memory_GameWon_part2" xml:space="preserve"> flips !</string>