[This bugreport involves both vte and gnome-terminal, tested with 0.11.11 and 2.
7.3.]

A set of so called "word characters" can be teached to vte, which influences
the behavior of mouse double click.

By default this is the empty string, which vte handles specially at the 
beginning of src/vte/vte_terminal_is_word_char(): all characters that are 
printable but not punctation or whitespace are treated as word characters. The 
result: words contain digits or alphabetic characters (even accented ones), this 
is nice, however, no other symbols are part of words, which might not fit my 
personal taste.

If word_chars is set to some non-emtpy value, this piece of code gets skipped, 
and only those characters explicitely mentioned are treated as word characters. 
This is the default of gnome-terminal, since it initializes this field of vte to 
a value taken from a gconf variable, the default value is -A-Za-z0-9,./?%&#:_

The big disadvantage is that this time accented letters are not treated as part 
of words, which is nonsense. Okay, I can list all the accented letters of my 
language, but I cannot list all the accented letters of all the languages, 
however, if I meet a foreign accented letter in my UTF-8 terminal, I still want 
it to be handled as a word char.

Which punctation symbols are word chars is up to my personal taste, so I'd like 
that one to remain configurable, however, whether a letter with an accent on it 
is word character is not a matter of taste, it is a fact: it _is_ a word 
character.

With the current situation this cannot be handled properly, and also the default 
setting of gnome-terminal is brain-damaged since double click stops the 
selection at accented letters. I can either clear this field in gnome-terminal's 
preferences and cope with the fact that none of the punctation symbols are word 
chars, or I can start listing all the accented characters I meet.

A quick and simple solution is to force vte to handle all alphanumeric 
characters as word characters. Patch follows for this solution. Then A-Za-z0-9 
could be dropped from the default value of word_chars in gnome-terminal
src/gnome-terminal.schemas since it becomes redundant.

A more proper but more complicated solution would be to change the interface:
instead of one word_chars setting of vte, it should have two fields: 
add_to_word_char and delete_from_word_char, so I can force a character to be a 
word_char and also I can force it not to be word_char, but for all the 
characters that are not specified in either fields, the default would be calling 
g_unichar_...() just like currently vte does if the word_chars field is empty.

(Also please note that handling the empty set specially for a field which is a 
set of particular elements is generally a bad design, since there's no way to 
specify an emtpy set.)