Add Serbian (cyrillic & latin) translation

[rammba]

Hello, as a current Serbian translator for N++, I wanted to translate context menu message as well.

I've noticed that translation was introduced in #25. However, since Serbian language is not that popular and widely used I wasn't sure how to implement this properly.

First thing, I didn't know which IBM code to use for cyrillic and latin version of serbian. Based on the IBM docs mentioned in the issue, or its latest version 6, I should use SRB for cyrillic and SRL for latin. However, when I looked into CultureInfo class, it's ThreeLetterWindowsLanguageName field says that SRO is for cyrillic and SRM for latin. I ended up using AFX_TARG_SRO and AFX_TARG_SRM, but I didn't found proper documentation for what should be used.

Second thing, I didn't succeed in finding documentation for SUBLANG_ values. I've used SUBLANG_SERBIAN_SERBIA_CYRILLIC and SUBLANG_SERBIAN_SERBIA_LATIN which should depend on sr-Cyrl-RS and sr-Latn-RS locales/cultures, but I'm not sure. Only clue that I had is winnt.h file that I have on my Windows 10, which has following content: part of winnt content.txt. There you can see comment stating: WARNING: This pattern is broken and not followed for all languages. Serbian, Bosnian & Croatian are a few examples. If you have any clue where this can be found online, it would be great.
Problem with that approach is how Visual Studio marks SUBLANG_SERBIAN_SERBIA_LATIN. For some reason, it doesn't recognize it as a normal string table, while cyrillic version is ok:

@GurliGebis, @xomx, @donho do you have any clue where to find documentation about these topics. Sorry, but I never worked that much deep with languages and locales, so I probably missed something.

[GurliGebis]

I must admit, I don't know enough about translations to figure this out.
@donho any ideas?

[donho]

@rammba

Here are the symbols I found in the header of VSStudio (ntdef.h):

...
#define SUBLANG_SAMI_SOUTHERN_SWEDEN                0x07    // Southern Sami (Sweden)
#define SUBLANG_SAMI_SKOLT_FINLAND                  0x08    // Skolt Sami (Finland)
#define SUBLANG_SAMI_INARI_FINLAND                  0x09    // Inari Sami (Finland)
#define SUBLANG_SANSKRIT_INDIA                      0x01    // Sanskrit (India) 0x044f sa-IN
#define SUBLANG_SCOTTISH_GAELIC                     0x01    // Scottish Gaelic (United Kingdom) 0x0491 gd-GB
#define SUBLANG_SERBIAN_BOSNIA_HERZEGOVINA_LATIN    0x06    // Serbian (Bosnia and Herzegovina - Latin)
#define SUBLANG_SERBIAN_BOSNIA_HERZEGOVINA_CYRILLIC 0x07    // Serbian (Bosnia and Herzegovina - Cyrillic)
#define SUBLANG_SERBIAN_MONTENEGRO_LATIN            0x0b    // Serbian (Montenegro - Latn)
#define SUBLANG_SERBIAN_MONTENEGRO_CYRILLIC         0x0c    // Serbian (Montenegro - Cyrillic)
#define SUBLANG_SERBIAN_SERBIA_LATIN                0x09    // Serbian (Serbia - Latin)
#define SUBLANG_SERBIAN_SERBIA_CYRILLIC             0x0a    // Serbian (Serbia - Cyrillic)
#define SUBLANG_SERBIAN_CROATIA                     0x01    // Croatian (Croatia) 0x041a hr-HR
#define SUBLANG_SERBIAN_LATIN                       0x02    // Serbian (Latin)
#define SUBLANG_SERBIAN_CYRILLIC                    0x03    // Serbian (Cyrillic)
#define SUBLANG_SINDHI_INDIA                        0x01    // Sindhi (India) reserved 0x0459
...

And your PR seems correct to me: