There are things professional translators have to bitterly face due to other professional translators' lack of knowledge on small things about Indonesian standard word. The worst thing happens when the project manager or the outsourcer does not understand Indonesian and they take all things for granted; the reviewer is always right or at least the second professional reviewing the first professional's is always with absolute knowledge of the target language. This assumption will lead to long debate and will result in an incorrect target language.
The only thing we can do is to give him as many valid links regarding the issue as possible. Client finally understood that the correct form is Beri tahu instead of Beritahu. We refer to http://kamusbahasaindonesia.org/beri%20tahu and http://bahasa.kemdiknas.go.id/kbbi/index.php and asked him to type Beri tahu and Beritahu to check the validity of both forms. So, there are hundreds of ways we can adopt to teach our client on the correct Indonesian without further debating.
For language outsourcers and project managers around the world, there should always be time and space to provide for us sitting together discussing this matter, so the product is always on track.
For professional translators, there is no end for us to learn all things replenishing our 'empty cup' and it is time for us to post the same issues regarding our native language for the non-native speakers to learn from.