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Basic idea is to sort the strings and compare signature of strings, where signature is the alphabetically sorted string.
What would be the efficient algorithm to do so ?
If you are sorting the UTF8 characters “alphabetically”, you can convert them to 32-bit integers (UTF8 chars are 1 to 4 8-bit values) and then do a RADIX sort. It will work in O(N) time. If you were using just ASCII, I would suggest Counting Sort.
There are many ways to match the signatures but I would use a Hash Table ( O(1) on average ) or a O(Lg N) structure such as Red-Black Trees or Skip-Lists.
To further speed up your string matching, you can compress these signatures by Run Length Encoding these UTF8 characters (since they’re sorted, the signature will be runs + gaps). Actually, you could compress them to use bit tags that represent 7-bit chars (most common), RLE runs, and longer literals (8-bit through 32-bit chars). Comparing the compressed strings would be faster.