In dutch language, the category-page is displayed different

Hi,

I’m German/Belgian, so please excuse me for bad English.

First of all: as a total beginner of WordPress I’m really happy to have found theme Attitude. I have just a little HTML knowledge, I dare to make little changes to the PHP-files :-). This theme was the right one for little adjustments to meet my needs.
So, thank you for this nice work!

I hope you could help me with the following:
Site is: PS-caballus.be
My site is as good as ready, almost everything is perfectly working.
I managed to show the slogan-‘line’ on every page, regardless how I select a page/post/category/search. (header_extensions: is_home, is_category etc)
The language of the site was first English, so I changed little things in PHP files to change the ‘read-more’-button and the searchbox (to Dutch words).
Then I discovered I can only change the months-names (in Archives-Widget) when I install the dutch language for WordPress. So I managed to change the site to Dutch. The text for ‘select month’ is in Dutch-language now, the month-names too. Perfect, I thought! I was totally happy ??

But then I saw that the Slogan-line (under menu, like home-page) was not showing in a category-page, when I select the ‘read-more’-button (verder lezen…).
Example
To test I changed the language back to English and yes: it’s working again.

My question is thus: can I somewhere (in Attitude-files) change the ‘select month’ and ‘month-names’ into Dutch when I keep the English settings?
Or how do I have to arrange to show again the Slogan-line on the category-page (when clicked on ‘read more’-button) when the website is in the Dutch-language?

Big thanks in advance!
S.