Speaking of things being written in a "somewhat weird fashion", I find this bothersome (even as corrected by almut):

while ($linein = <FILEIN2>) {
    chomp $linein;
    @arrayin = split /:/, $linein;

    if (exists $arrayin[0] && $arrayin[0] eq "Default")
    {
        $englishword = trim( $arrayin[1] );
    }
    if (exists $arrayin[0] && $arrayin[0] eq "Spanish_LatinAmerican|es
+_MX")
    {
        $spanishword = trim( $arrayin[1] );
    }
    if (exists $arrayin[0] && $arrayin[0] eq "Spanish_LatinAmerican|es
+_MX")
    {        
        $langhash{$spanishword} = $englishword;
    }
}
[download]

I think this would make more sense:

while (<FILEIN2>)
{
    next unless ( /.:\s*\S/ );  # necessary/sufficient condition for w
+hat follows

    my ( $lang, $text ) = split /:/, $_, 2;
    if ( $lang eq "Default" )
    {
        $englishword = trim( $text ); # takes care of chomping
    }
    elsif ( $lang eq "Spanish_LatinAmerican|es_MX" )
    {
        $spanishword = trim( $text );
        $langhash{$spanishword} = $englishword;
    }
}
[download]

It seemed to me that the OP code was doing too many unnecessary tests with all those "if" conditions, and they actually weren't entirely appropriate to the task: you only check for the existence of the first array element, and then do something with the second array element whether it exists or not.

And I would agree with the Anonymonk who thinks that "weird" is an understatement when describing a subroutine with a for loop that does a "return" on each iteration... {grin}