How do you get the w with circumflex - my (Android) keyboard doesn't offer an alternative character for w other than the digit 2. (Same applies to Y).
There should be on screen buttons under the text box (at least there is on PC), otherwise you can download "Swiftkey" which has a Welsh option which will allow you to insert the Y and W with circumflexes.
I have the same problem. I get around it by typing a regular w then using the auto-correct feature to choose the correct word from the Welsh spell-check Dictionary.
For anyone else reading later: On OS X, with a Welsh keyboard, it's alt+w. On Ubuntu Linux with a UK keyboard it's alt+[, then press w.
On windows you can also download 'to Bach' which will allow you to type those characters on a UK keyboard on windows
This Android app gives you access to all the accents (just do a long press when you need one and the accents become available)
On Android you need to add a Welsh keyboard under Settings - Language & Input then select it as the current keyboard. With mine I can switch between English and Welsh keyboards by pressing and holding the space bar.