
  or it will just install ubuntu as a program in windows??


Indeed. Wubi will install it as a program in Windows. This will make Ubuntu slower and dependent on Windows.

If you don't want to install as a program in Windows, you should follow these instructions.

Will installing Ubuntu using Wubi erase Windows?
I prove to install this plugin following the instructions of this post: HTML pair tag highlight alternative for Geany editor on Ubuntu 14.04

but, when I write

sed -i 's/1.24/1.23/' wscript


it says me this:

fatal: destination path 'geany-plugins' already exists and is not an empty directory.


What can I do?

after 

./waf configure --enable-plugins=pairtaghighlighter


it appears me this:

Setting top to                           : /tmp/geany-plugins 
Setting out to                           : /tmp/geany-plugins/_build_ 
Checking for waf version in 1.6.1-1.7.0  : ok 
Checking for 'gcc' (c compiler)          : /usr/bin/gcc 
Checking for program pkg-config          : /usr/bin/pkg-config 
Checking for 'gtk+-2.0' &gt;= 2.16.0        : not found 
The configuration failed
(complete log in /tmp/geany-plugins/_build_/config.log)

