The nano editor provides syntax highlighting for a few languages and scripts by itself. Check out /usr/share/nano/

nits@nits-excalibur:~$ ls /usr/share/nano/

asm.nanorc     fortran.nanorc   man.nanorc     ocaml.nanorc   ruby.nanorc

awk.nanorc     gentoo.nanorc    mgp.nanorc     patch.nanorc   sh.nanorc

c.nanorc       groff.nanorc     mutt.nanorc    perl.nanorc    tcl.nanorc

cmake.nanorc   html.nanorc      nano-menu.xpm  php.nanorc     tex.nanorc

css.nanorc     java.nanorc      nanorc.nanorc  pov.nanorc     xml.nanorc

debian.nanorc  makefile.nanorc  objc.nanorc    python.nanorc

Link them to your user's nano configuration file (present at ~/.nanorc, ${XDG_CONFIG_HOME}/nano/nanorc, or ~/.config/nano/nanorc, whichever is encountered first) with something similiar to this line:

nits@nits-excalibur:~$ cat ~/.nanorc

include /usr/share/nano/sh.nanorc

Now, syntax highlighting is enabled in nano for whatever file you linked (You could also link multiple files)

Note: Sometimes you might get a segmentation fault after you have edited your ~/.nanorc file. If such an error occurs, unsetting the LANG environment variable helps. You can unset it with unset LANG in the terminal. (Solution obtained from here)

There are also other solutions if you are not satisfied with your bash highlighting. One example of such can be found here

You can also write include /usr/share/nano/* to the ~/.nanorc file to enable all languages to be highlighted if your nano version supports it.