Yah!
This is due to your current language file is not complete, or these words are not defined in your language file.
You can find the language file for JoomDoc component in *JoomlaDirectory*/Components/com_joomdoc/views/themes/default/language/*YourLanguageName*.php
Simply add lines in the file, such as:
define('_DML_TPL_CAT_VIEW', "Downloads Home");
define('_DML_TPL_CATS', "Categories");
The later section eg: "Downloads Home" or "Categories" can be edited for your language. The front section eg: '_DML_TPL_CAT_VIEW' must not be altered or edited.
If you don't have the language file, simply copy english.php into *YourLanguageName*.php and edit the file.