I was able to create a form with default and custom form widgets in multiple languages successfully, so could you please give us more details for the error you receive and steps to reproduce it.? Do you receive the error when creating the form or when it is associated in the poll widget?
You can change the name for developers within the form control, or check the default suffix which is generated for every control. By default it is _C001. You can see it from Advanced settings -> ClientTemplateSuffix. You can then get or set the name for developers this way:
FormCheckboxes checkBoxControl = control
nameForDev = checkBoxControl.DataFieldName;
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Sitefinity CMS Ideas&Feedback Portal
and vote to affect the priority of the items