Only the Irish-language versions of placenames may be used on road and street signs in the State's Gaeltacht districts from today.
The definitive large-scale Ordnance Survey maps for these areas will give only the authoritative version of the Irish name.
Some 2,319 townlands from all the Gaeltacht areas in the State are covered by the legislation under the Placenames (Ceantair Ghaeltachta) Order 2004, which comes into effect today.
It means that the English versions of such placenames as Dunquinn and Ventry in the west Kerry Gaeltacht on the Dingle peninsula no longer have legal standing. Although the order does not affect private use of the English versions, the Irish-language Dun Chaoin and Ceann Trá will have to be used in statutory instruments and on road and street signs.
Large-scale OS maps produced from now on will only have Irish names and the provision will be extended to cover other maps "over a period of time", according to a statement from Minister for Community, Rural and Gaeltacht Affairs Eamon Ó Cuív.
A second order coming into effect today confirms for the first time the Irish-language versions of names of postal towns outside Gaeltacht districts. This order - the Placenames (Centres of Population and Districts) Order 2005, signed into law in February - means that an Irish-language name is now official alongside the English-language version in non-Gaeltacht areas.
For example, the Irish-language name for Mountcharles in Co Donegal is no longer Moin Séarlas, but Tamhnach an tSalainn, as this was the Irish-language version most commonly used locally and its historic name.
Irish-language names were given official recognition for the first time in the Official Languages Act of 2003. Irish placenames are being put on an equal footing on a county-by-county basis. So far, nine placename orders confirming the official Irish-language versions of placenames have been signed by Mr Ó Cúiv. These are for counties Kilkenny, Louth, Limerick, Monaghan, Waterford and Offaly as well as the Gaeltacht districts. The orders covering counties Dublin, Galway and Tipperary are almost complete.
Brendan Mac Gearailt, author and member of Údarás na Gaeltachta for Kerry, said that this was something which should have been done 100 years ago.
Mr Mac Gearailt, who has written books on Irish blessings and curses, and is currently compiling a book on placenames, commented: "The main annoyance for me is that the maps quite regularly did not coincide with signs. I don't want to see local tourists and anglers being led astray any longer."
In most cases, English placenames had come into use because the English did not pronounce the names properly and "came up with a load of garbage" which was then put on signs, Mr Mac Gearailt added. Under this confusion, Cill Airne became Killarney.