codestyling

Your are kidding me, isn’t it ?
_e('Sales in ', 'td') . _e('USA');
Running this code is useless, because what should the concatination of strings do? The function _e() echos the result immediately and returns nothing for concatination. Depending on where this is running, you will see either never the USA terms, because the code runs at a filter prior to the started output (and you can’t set the HTTP header afterwards) or if it runs inside a templates code, you would get at least:

Vendas em USA

All other outputs you may get are depending on interaction of installed plugins like qTranslate, WPML or others, they may translate some terms under the hood. Having no plugins running and using the normal WordPress standard theme for your blog, you will never get USA translated.
And furthermore USA is not a term of WordPress itself. The core doesn’t use it.

To complete the subject, my plugin is able to support mixed textdomains, you can use it by loading both textdomains.
As you may also notice, you will get the generate mo-file button for the “second_texdomain” too. By pressing it, my plugin generates a second file only containing those translations.

Extend the plugin’s code to:

<?php
/*
Plugin Name: Test the Textdomains
*/

load_plugin_textdomain('first_textdomain', PLUGINDIR,  '');
load_plugin_textdomain('second_textdomain', PLUGINDIR,  '');

add_filter('the_content', 'append_paragraph');
function append_paragraph($content) {
	return $content.'<p>'.__('Hello', 'first_textdomain').' '.__('World.','second_textdomain').'</p>';
}

you will get the translation as:
<p>Say Yes.</p>

Because my plugin is able to generate two files:

first_textdomain-de_DE.mo
second_textdomain-de_DE.mo

and assumed you load both textdomains, than you get the expected results. This is an advance feature and can be used to split backend only strings from frontend only strings.

This speeds up the page load on frontend, because normally the ammount of backend strings is in most cases dramatically higher than frontend strings (big plugins have approx. 700 strings but only approx. 30 used at frontend).
Using this feature allows to load one of the textdomains only at backend and avoids at the above example string count the pollution of memory with 670 strings never used for frontend rendering.

i need an example and the full error message (containing line numbers etc.)

Has been implemented with version 1.99.17 and works now along with the additional Microsoft API as you want it.

Texts within the “standard” Textdomain are stored into the *.po file but doesn’t need to be translated nor they will become part of the generated *.mo file. The plugin only uses the targets textdomain and the directly related strings to create the translation file.

Seems that your server uses a different user for FTP and PHP execution. This may affect files uploaded by FTP and modified by PHP. Downloaded plugins and themes within WordPress by PHP should be translatable.
This problem will be solved in future versions.

Has been solve with version 1.99.17 and enables now Google Translate V2 API and Microsoft Translate Service.

I’m currently working on a draft spec how to solve this backup issue. It’s not that easy to handle all for none programming related user.