What language is this word?
Retina, 51 bytes

.*[aeio]$
1
A`en$|ch|ei|au
^$
2
A`[jkz]|gy|m$
\D+
4


I came up with the regexes and @MartinBüttner did the conversion to/golfing in Retina so ... hurray for team effort?

The mapping is 1 -&gt; Italian, 2 -&gt; German, (empty) -&gt; Hungarian, 4  -&gt; English, with the amount classified in each category being 4506 + 1852 + 2092 + 3560 = 12010.

Try it online! | Modified multiline version

Explanation

First off, the equivalent Python is something like this:

import re
def f(s):
  if re.search("[aeio]$", s):
    return 1
  if re.search("en$|ch|ei|au", s):
    return 2
  if re.search("[jkz]|gy|m$", s):
    return ""
  return 4


Let me just say that o$ is an excellent indicator of Italian.

The Retina version is similar, with pairs of lines forming replacement stages. For example, the first two lines

.*[aeio]$
1


replaces matches of the first line with the contents of the second.

The next three lines do the same, but using Retina's anti-grep mode - anti-grep (specified with A`) removes the line if it matches the given regex, and the following two lines is a replacement from an empty line to the desired output.

A`en$|ch|ei|au
^$
2


The following line uses anti-grep again, but doesn't replace the empty line, giving the fixed output for Hungarian.

A`[jkz]|gy|m$


Finally, the last two lines

\D+
4


replaces a non-empty non-digit line with 4. All of the substitutions can only happen if no previous substitution activated, simulating an if/else if chain.