[Koha] Can't locate LangInstaller.pm in @INC

[Mark Alexander]

> > root at srv2:/usr/share/koha/misc/translator# perl -I/usr/share/koha/misc/translator translate install it-IT
> > Can't locate TmplTokenizer.pm in @INC (you may need to install the TmplTokenizer module) (@INC contains: /usr/share/koha/lib /etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.24.1 /usr/local/share/perl/5.24.1 /usr/lib/x86_64-linux-gnu/perl5/5.24 /usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.24 /usr/share/perl/5.24 /usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base) at /usr/share/koha/misc/translator/tmpl_process3.pl line 20.
[...]
> sudo koha-shell instancename

This problem comes up so frequently that I wonder if the scripts
could check for it and suggest a fix, along these lines:

if (!defined($ENV{KOHA_CONF}) && !defined($ENV{PERL5LIB})) {
   die("Please run koha-shell first.");
}