Hi,
I gather that you want to know two things - the different ways in which you can impart training to your Business Development Managers and how to communicate the importance of this training.
To answer the first question: Depending on how many managers you need to communicate the importance of the training to, you can either hold a meeting in which you explain the importance, why you need to do it, how it will help the business grow, etc. (this works if you are addressing a group of not more than 20). Also, allow them to ask questions so that you can resolve their worries.
If you have more managers, you may want to send a detailed email explaining the situation and inviting suggestions, contributions, doubts, and ensure that you resolve the same.
To answer the second question: Language training is most effective when they can listen and reproduce the sounds of the language and when they can be corrected immediately - ideally in a one-on-one setting or one-to-20 setting.
Warm Regards,
Rupa
9820314311
Trainer