It is legitimate (and currently lawful) to insist on the use of a sole common language in the workplace. You would want to do this to ensure good communication, avoid suspicion between different groups and facilitate good working relationships. In Wales this language could be Welsh, although advice should be sought from the Welsh Language Commissioner first. In the rest of the UK this would normally be English and you can set a policy as such.
Your policy might specify the areas of the workplace where employees need, or must attempt to use, English. Usually this would include office areas and any shop floor. But you may want to consider extending it to communal areas such as the canteen, the car park or even the toilets. If you allow other languages to be spoken in these latter areas you risk division in your staff or workforce – but it may be a balance between the suspicion use of a non-english creates and welcoming people who may have enough stresses with which to cope already.
You may want to consider the needs of differing groups
Those for whom English is their first language or who are fluent
This group should be required to treat other groups with respect and to recognise that broken English can seem more direct than the speaker may intend. As an employer you have a vicarious liability (i.e. a liability transferred from your employees to you) for discrimination, which could be in the form of harassment, in the workplace.
Employees who have a second language may reasonably be expected to assist in translation or interpretation.
Employees who have a good grasp of English as a second or later language
Your policy can reasonable require these employees to communicate in English. Again they may reasonably be expected to assist in translation or interpretation.
Employees learning English
While such employees may be required to speak in English or attempt to do so exceptions may be considered.
Exceptions
You should provide a translator to enable an alternative language to be used in conjunction with English in the following circumstances:
- Job interviews
- Induction
- Health and Safety
- Essential instructions
- Communicating expectations
- Emergencies
- Formal discipline or grievance matters
Where matters are not straightforward it would be safer to engage an interpreter to ensure better communication and therefore understanding.
Learning English
You might want to consider whether to assist non-English speakers to acquire the language perhaps by providing in-house tuition or encouraging or financing enrolment at a local training provider.