For this you have to remember that in Wales there are estimated to be about 562,000 Welch speakers that is supported by only 10 Welch congregations. There are in comparison 41 English congregation in Wales. So there won't be a lot of elders who speak Welch so they are needing to be able to play a recorded talk because it has to be given all in the same night.
That's because the majority of Welsh speakers speak English. The number of people who only speak Welsh is much, much smaller (if they exist at all - god, that's child abuse if it is).
Many years ago I worked on websites for the Welsh Assembly (the regional government). The number visiting the Welsh language versions of pages was very small compared to the English version.
Welsh is also artificially kept alive and pushed by the government ... which is something the WTS takes advantage of and probably gets some grant money for when they do "local language" endeavours like this.