It really does not matter what the language settings in the Control Panel's 'Regional Settings' pane is.
My 'Regional Settings' is English; but, this does not mean much, on which I'll elaborate a little later.
'DOTTED CAPITAL I' and 'DOTLESS SMALL I' are only peculiar to Turkish/Turkic languages so, whenever you encounter them, there is only one way to do proper case conversion.
i.e.
Lowercase(DOTTED CAPITAL I) --> DOTTED SMALL I
Uppercase(DOTLESS SMALL I) --> DOTLESS CAPITAL I
This is always valid (and simpler to implement) for all texts.
Yet, only if you do know that that particular (piece of) text is in Turkish, can you assume the following to be valid:
Lowercase(DOTLESS CAPITAL I) --> DOTLESS SMALL I
In order to handle this 'quirk', it will require TextPad to have a 'per selection' flag that the user needs to set before properly lovercasing the selected text.
And, no, TextPad cannot rely on the global 'Regional Settings'; neither does having a TextPad-global setting help, nor is a 'per document' setting is useful. It has to be 'per selection'.
And the reason is simple: Since we are now all dealing with Unicode, the whole text could a mixture of languages with just a portion of it in Turkish.
Actually, this sort of thing (i.e., language-dependent case conversion) is not peculiar to Turkish. There a quite a few others (Spanish, Dutch, even German to name a few) which TextPad needs to cater for.
Who said Unicoding a text editor would simply be letting fonts from different locales display nicely
