Welsh-language versions of two leading computer programs have been released by the Welsh Language Board and Microsoft.
Croeso i Windows yn Gymraeg - or welcome to Welsh Windows
People using computers can now choose to have Windows XP and Office 2003 in Welsh.
Meri Huws, chair of the Welsh Language Board, said it was "a very important development for the Welsh language".
Welsh is one of 40 new languages being added, in response to complaints from around the world that youngsters were losing their native tongues.
The work, which took 15 months to complete, translated half a million Welsh words and phrases.
The Welsh Language Interface Packs (LIPs) see the Welsh language joining other computer languages such as Hindi, Irish and Maori.
The software will be available to download free through the Welsh Language Board and Microsoft websites and on CDs from the Welsh Language Board.
Beverley Lennon, a Welsh language teacher at Cantonian High School in Cardiff, has tried out the system and said her pupils would benefit from it.
She said: "What's lovely about this is, as opposed to the children seeing the Welsh words in a book, they are going to be going on to a screen and seeing and learning so many different words in Welsh and learning how to actually do things through the medium of Welsh.
"You have a lot of key words on here like 'gyda,' which means with, 'agor' which means to open.
"Again, they are going to recognise the key words. I know they are going to be very excited."
Welcoming the software, Welsh Language Minister Alun Pugh, said: "The launch of Windows and Office 2003 in Welsh marks a real milestone for the language and fits in well with the Welsh Assembly Government's vision for a bilingual Wales.
"I find it very encouraging that at a time of increasing globalisation, a huge multinational company still recognises the importance of supporting diversity in languages and culture."
Ms Huws said: "This is without doubt a very important development for the Welsh language and confirms that the language is contemporary, relevant and useful.
"Having familiar computer programmes such as Word and Outlook available in Welsh will increase the opportunities for people of all ages to use the language in their everyday lives, both at work and at home."