Here's how you could change Quick Search to something else by overriding the template:
Create a folder called templates in the Sphinx project directory.
Copy <Sphinx install dir>/themes/basic/searchbox.html into templates .
In conf.py add
templates_path = ["templates"]
Rename “Quick Search” to everything you need in a copy of searchbox.html .
But I wouldn’t do that.
A more flexible approach is to create a gettext MO file and configure the configuration described in the documentation for locale_dirs . Like this:
The <Sphinx install dir>/locale/sphinx.pot template file contains all the lines that can be translated. Copy this file to the local sphinx.po file.
Add your changes to sphinx.po .
Use msgfmt.py to compile sphinx.po into sphinx.mo .
Place sphinx.mo in the appropriate directory ( <your_locale_dir>/en/LC_MESSAGES for English).
See also http://docs.python.org/library/gettext.html#internationalizing-your-programs-and-modules .