User-519136805 posted
There is no way which is fast & easy to convert current application in multi-lingual site.
Effort needed in conversion is depends on how existing system has been maintained. if there is no such precausion steps taken care during early days of development than it will be difficult task to convert it in multi-lingual.
As of now , you can create checklist & decide where major changes required to convert existing app in ML (multilingual).
Once you have the checklist , you will be able to decide which approach will be appropriate for you.
Hope this will help !!!