I feel very sorry about your unsatisfied experience about our tour guide.
Tour guide - Wee is actually a bilingual tour guide with certificate. I am not sure about the reason of why he didn't take the English certificate during the day's service. But it is undeniable that Asian people have local accent when speaking English. This situation is acceptable for most of our guests who come from Engish-speaking countries but it might, sometimes, cause inconvenience for guests who command many different languages.
I also noticed that you are from Germany. Would it be better if we arranged a German speaking tour guide for you in another chances to show you around Singapore.
Anyway, please accept our sincere apology, if there is anything we can do to make this unpleasant part of service as small as possible in your impression about Singapore. Please do let us know. :)