Doc: rename HOWTO_compile_lang_files.md

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docs/compiling_lang_files.md

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+# How to compile lang files (OpenTTD and strgen)
+
+Last updated:    2009-06-30
+
+## strgen usage
+
+This guide is only interesting for people who want to alter something
+themselves without access to [translator.openttd.org](https://translator.openttd.org/).
+
+Please note that your compiled language file will only be compatible with the OpenTTD version
+you have downloaded `english.txt`, the master language file, for. While this is
+not always true, namely when changes in the code have not touched language
+files, your safest bet is to assume this 'limitation'.
+
+As a first step you need to compile strgen. This is as easy as typing
+`'make strgen'`. You can download the precompile strgen from:
+[http://www.openttd.org/download-strgen](http://www.openttd.org/download-strgen)
+
+strgen takes as argument a txt file and translates it to a lng file, allowing
+it to be used inside OpenTTD. strgen needs the master language file
+`english.txt` to work. Below are some examples of strgen usage.
+
+## Examples
+
+### Example 1
+
+If you are in the root of your working copy (git repository), you should type
+`./strgen/strgen -s lang lang/english.txt`
+to compile `english.txt` into `english.lng`. It will be placed in the lang dir.
+
+### Example 2
+
+You only have the strgen executable (no working copy) and you want to compile
+a txt file in the same directory. You should type
+`./strgen english.txt`
+and you will get and `english.lng` in the same dir.
+
+### Example 3
+
+You have strgen somewhere, `english.txt` in `/usr/openttd/lang` and you want the
+resulting language file to go to /tmp. Use
+`./strgen -s /usr/openttd/lang -d /tmp english.txt`
+
+You can interchange `english.txt` to whichever language you want to generate a
+.lng file for.
+
+## strgen command switches
+
+`-v | --version`
+strgen will tell what git revision it was last modified
+
+`-t | --todo`
+strgen will add <TODO> to any untranslated/missing strings and use the english
+strings while compiling the language file
+
+`-w | --warning`
+strgen will print any missing strings or wrongly translated (bad format)
+to standard error output(stderr)
+
+`-h | --help | -?`
+Print out a summarized help message explaining these switches
+
+`-s | --source_dir`
+strgen will search for the master file english.txt in the directory specified
+by this switch instead of the current directory
+
+`-d | --dest_dir`
+strgen will put <language>.lng in the directory specified by this switch; if
+no dest_dir is given, output is the same as source_dir