A lady at Radio Bremen tells me that their online Plattdeutsch course will begin on September 29th.
Here is a link to it:
The page is not ready yet,but you can save the link,and start using it on the 29th.
Just in case...
The people that can know whether they are Celtic or not,with the highest level of certainty,would be the folks that are R1b-M222.
A large chunk of the population of Western Ireland has the M222 marker,and it's a good guess that you had Irish ancestors,if you have this marker.
Would it be accurate to say,that any citizen of Germany could speak Hochdeutsch,because it is 'standard'-but that many Hochdeutsch speakers would find it difficult or impossible to understand Plattdeutsch?
And what's your Y and/or mt haplogroup?
My Y haplogroup is commonly referred to these days as R1b-U106*.
At present,I don't fit in any of the subclades,the major one being L-48+.
We have a new Walk The Y project at FTDNA,for searching for new Y SNP's in U106's that are negative for L-48.