Just as I thought. You can’t produce evidence for your claim. Thanks for playing though.
The long and short of it is that all members of Abba had English as their second language from a young age, their primary language of course, being Swedish.
While they were considered proficient in England, some of the members had difficulty singing in English, due to the phrasing and pronunciation of certain words. It does not appear to be stated in the article that cue cards were ever used but it seems likely that during recording at least, they had lyric sheets in which certain English words were phonetically spelled out so that they would not have as many mistakes when recording.
Still, especially on their ealier songs, you could hear that there were not particularly comfortable singing in the English language. Check out the Swedish version of "Waterloo" and compared with the familiar English version and you will see what I mean. They were much more comfortable and relaxed singing in their native language. The English version comes off as fairly stilted and stiff by comparison.
Here is the article I alluded to earlier that is quite lengthy.