Po
PO files are the files which contain the actual translations. Each language will have its own PO file, for example, for French there would be a fr.po file, for german there would be a de.po, for American English there might be en-US.po. You can even use po files to customise the displayed text without changing the code, by for example, creating an adapted file such as en-my_company.po.
The core of each PO file is very simple; it is made of simply pairs of the source text - that which is found in the code - and target text, the text which is wanted in the translation. For example, in the French PO file you might have a translation of a string as follows:
POT file
POT files are basically the template files for PO files (Warning: Microsoft also uses POT as the extension for PowerPoint template files, but these are not the same). They will have all the translation strings (the msgstr parts) left empty, for example:
ko_KR Header
"Project-Id-Version: WORLD\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2015-06-07 13:16+0900\n"
"PO-Revision-Date: 2015-06-07 13:17+0900\n"
"Last-Translator: yourname <[email protected]>\n"
"Language-Team: yourname <[email protected]>\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"X-Generator: Poedit 1.8.1\n"
"X-Poedit-Basepath: .\n"
"Plural-Forms: nplurals=1; plural=0;\n"
"Language: ko_KR\n"