The main reason many people struggle to communicate effectively in English is not bad grammar!
The chances are, that they know so-called English grammar inside out and have top grades. The problem is, they haven’t learnt the stress patterns or how we use words in predictable phrases that ‘sound’ right to native speakers.
They might come across as abrupt or impolite to native speakers, not because the words are incorrect. It’s just a lack of awareness of culture and the nuances of influencing and negotiating. What they need is not more English lessons or grammar exercises.
The need role models, a good mentor and lots of listening. Do you have people in your organisation who could do with some guidance?