The language in which weekday and month names will be displayed is specified in the date_locale setting in the configuration maintenance panel.
If the locale is empty or invalid, the date will be displayed in your system’s default language (usually English). The TalkBack installer will set this field to be the same as the language you selected during installation. That language name may or may not be a valid locale code. So you may have to follow the below instructions to find a valid code for non-English languages.
You can tell if you have set the right code for your language by looking at the admin date and comments template date fields in the admin configuration maintenance panel.
The locale setting entry may be constructed as: a two character language code (en), a language code and country code combination (en_US or en_UK), a three character language code (eng), a language name (english).
Unix type operating systems use language names and codes from the ISO-639 specification. Windows server users see this MSDN website.
Some systems may require a language code/country code combination (en_US). Some may require that a character set identifier be appended (examples: en_US.ISO8859-1 or en_US.UTF-8).
You may need to do a little trial and error experimenting to get dates to display properly in your language. As an example, for the Dutch language, try entering each of the following into the TalkBack date locale setting until you find one that works:
dutch
dut
nl_NL
nld_NLD
nl_NL.UTF-8
nl_NL.ISO8859-1
nld_NLD.UTF-8
nld_NLD.ISO8859-1
If you are unable to find a string that works, contact your web host technical support and ask them if your language is installed and, if so, what PHP locale string to use for setting the locale.