[ticket/11328] Add language variables for buttons

New language variables for buttons

PHPBB3-11328
[ticket/11328] Replace long buttons text with short text

Replace long buttons text with short text, like it was on images

PHPBB3-11328
Merge remote-tracking branch 'remotes/cyberalien/ticket/11328' into develop

# By Vjacheslav Trushkin
# Via Vjacheslav Trushkin
* remotes/cyberalien/ticket/11328:
  [ticket/11328] Replace long buttons text with short text
  [ticket/11328] Add language variables for buttons