Using the advice I've now simplified:

You've still got the same look-behind typos as described in Re: Looking for a cleaner regex

Guessing at the meaning the look behinds, the list of words is now 

.ron
steis
ste
mos
es
o
ó
í
ué
(?<!u)é
(?<!st)e
(?<!ro)n
(?<!.is)s
(?<!mos)s
(?<!eis)is
(?<!ste)is

[download]

Eliminating the obviously needless look-behinds , leaving the goofy guesses and guessing again 

.ron
steis
ste
mos
es
o
ó
í
ué
é
e
n
(?<!.is)s  ## maybe meant (?<!.i)s
(?<!mos)s  ## maybe meant (?<!mo)s 
(?<!eis)is ## maybe meant (?<!e)is
(?<!ste)is ## maybe meant (?<!ste)is

[download]

If my new guess is correct the last 4 needless look behinds can be replaced by "s" 

steis
.ron
ste
mos
es
ué
o
ó
í
é
e
n
s

[download]

And the single character suffix can be replaced by a char class 

steis
.ron
ste
mos
es
ué
[oóíéens]

[download]

So there you have it the optimal regex is  qr/( .ron | steis | ste | mos | es | ué | [oóíéens] )$/x

In reply to Re: Looking for a cleaner regex by Anonymous Monk
in thread Looking for a cleaner regex by k-man

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.