The first, why we must remember what you have the GPSMAP620? Garmin have so many different model!

The main - try this (where do find "layout"?:

<str>
<tag>TXT_Keyboard_Mode_STR_M</tag>
<txt>Язык клавиатуры</txt>
</str>
<str>
<tag>TXT_Keyboard_Mode_STR_S</tag>
<txt>Раскл.клав.</txt>
</str>
<str>
<tag>TXT_Keyboard_Mode_STR_T</tag>
<txt>Раскладка клавиатуры</txt>
</str>
<str>
<tag>TXT_Keyboard_STR_S</tag>
<txt>Клавиатура</txt>
</str>