BuddyPress.org

11. Do you have any custom functions in bp-custom.php? Yes, the function from every tutorial talking about the language, but changed for my custom language file.

Which tutorial are you telling about ?

Remove that function, it’s not necessary i guess.

By default, you set your site language in wp-config define ( ‘WP_LANG’, ‘de_DE’ ); and in wp settings > general (depending if single or MS install)

Where to put the translation ?
wp-content/languages/de_DE.mo (this is the WP translation)
wp-content/languages/plugins/buddypress-de_DE.mo (this is the BP translation)
wp-content/languages/themes/theme_name-de_DE.mo (this is the theme translation)

You say you used gedit to generate your translation. It’s a text-editor, not a mo compiler. (mo means machine only, you can’t read it !)

I suggest that you use poEdit to make a translation and generate a correct mo file.
On Ubuntu, you can (not sure) use the msgmt command from the gettext package. Something like this

$> msgfmt -o your_file.mo -v your_file.po

I just tested Duena and the BP translation is fine.

Recheck your po/mo files. Here what you must have:

duena – leave as is.
buddypress/bp-languages/buddypress.pot
wp-config – if you use english, as it’s default language you have nothing to do
// define(‘WP_LANG’, ” );
wp-content/languages/plugins/buddypress-en_US.mo

Now if you want to modify only some strings, make a copy of the pot file and put it in a folder outside of buddypress.

From this copy you remove anything you don’t want and keep only the 2 lines or 4 lines (if plural form) who belong to the string you want to change. You keep only the string you want to change.
Once done, save and rename it buddypress-en_US.po and open it with a text editor (not poEdit), as we’re going to modify the header.

msgid ""
msgstr ""
"PO-Revision-Date: 2014-09-12 00:05+0100\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Plural-Forms: nplurals=2; plural=n > 1;\n"
"X-Generator: Poedit 1.5.7\n"
"Project-Id-Version: BuddyPress 2.0.2\n"
"POT-Creation-Date: \n"
"Last-Translator: \n"
"Language-Team: \n"
"Language: en\n"
"X-Poedit-SourceCharset: UTF-8\n"
"X-Poedit-Basepath: .\n"
"X-Poedit-KeywordsList: __;_e;__ngettext:1,2;_n:1,2;__ngettext_noop:1,2;"
"_n_noop:1,2;_x:1,2c;_nx:4c,1,2;_nx_noop:4c,1,2;_ex:1,2c;esc_attr__;"
"esc_attr_e;esc_attr_x:1,2c;esc_html__;esc_html_e;esc_html_x:1,2c\n"
"X-Poedit-SearchPath-0: ..\n"

The rest of the file looks like this:

msgid "Friendships"
msgstr ""  <strong><- replacement goes here</strong>

#: bp-friends/bp-friends-template.php:588
msgid "%s friend"
msgid_plural "%s friends"
msgstr[0] ""
msgstr[1] ""

Save in text format utf8 without BOM. (important)

Now you can open this po file with poEdit, do your translation and save so that poEdit generate a mo file (see poEdit settings first to get this automatically each time you save a file).

Copy the mo file in the appropriate folder and, normally, you’re done.

References
https://codex.wordpress.org/Translating_WordPress
https://make.wordpress.org/polyglots/handbook/translating/basics/
http://www.wpbeginner.com/wp-tutorials/how-to-disable-automatic-updates-in-wordpress/

The definitive guide to disabling auto updates in WordPress 3.7

Glad you got it to work !

FYI: BP Poke comes with his own languages folder who contains po/mo in english. This is wrong, but has no influence if you want to use another language.

The reason is that many authors create a po file instead of a pot file, and when they save the file, poEdit (or similar) automatically creates a mo file.
The correct file name should be bp-poke.pot ! You can remove the original – in english – mo, totally useless: the plugin is coded in english !

To use a translation for this plugin, you add xx_XX.mo to bp-poke/languages/xx_XX.mo

Text domain ref: bp-poke.php:50

You’re welcome !