"Sorry, I am tired."
Translation:Sori, dw i wedi blino.
Of course it isn't really fair to compare the grammar of two different languages anyway, but in English you have ''aren't"- contraction of 'are n[o]t', "haven't" for 'have n[o]t' and others. There's even "shan't" for sha[ll] n[o]t' if you want an example with multiple contracted words, or "tis" for one that's completely identical to this instance. Whether "dwi" should have an apostrophe at the start is another argument entirely!
You make a valid point as the comparison of two languages isn't good. One question though, as my welsh grammar isn't great. Would the concatenation of three words be valid such as "dw'i'n". It just doesn't seem right to use put "dw" and "i" together. Also 'tis begins with an apostrophe to denote it's a contracted word. I'm just under the assumption that it's do-able, it's just grammatically incorrect.
To be honest, I think we'd probably have to get hold of a professional welsh linguist or something to resolve this.
It isn't a lingustic approach, but if you Google for "dw i'n" and for "dwi'n" (being sure to use the quotes to get an exact match), "dwi'n" actually beats "dw i'n". Can't find any formal writing making it clear, but from personal experience "dwi'n" is definitely used by natives just as often as "dw i'n", if not more so. It could come down to a north / south divide thing as things often do with Welsh, but as a native south Walian I know which side I'm on!
I did some research and found out it comes down to mutations from the original form which is "ydwyf i". All variations are valid and depend on regions as you suggested but a lot more than just south/north. Turns out it's regional to the point of Cardiff and Swansea use different variations. I'm a native south Walian from the Morganwg region and I've only ever seen "dw i'n" here. So when it comes down to it, use whatever you want.