In the directory where PHP is installed I have created a php.ini file and verified that configuration files are coming from the php.ini. Extensions that are missing are enabled like so:
extension=mbstring
extension=fileinfo
extension=intl
php_mbstring.dll, php_fileinfo.dll and php_intl.dll files are present in the ext directory. How can I troubleshot this problem further? I have looked for answers: here and here.
edit
I have also edited php.ini-development and php.ini-production uncommenting the relevant extensions from above. The mbstring.dll was downloaded from here. I unzipped the dll to php-directory/ext
The problem I encountered was a bit special. I found an answer here. Apparently there are 4 files icu****.dll in the PHP executable directory. After copying those to the bin directory of Apache Server, the extensions worked.