Two scripts (Han and Cyrillic) comprise 90% of top level IDN registrations.
Historic factors are also relevant in this comparison: only in 2009 were ccTLDs given the opportunity to apply for their IDN equivalents, and the Russian top level IDN, рф, was one of the first IDN ccTLDs to be launched that year. It has sustained high volumes ever since. Overall, there is slightly greater script diversity to be found in second level IDNs, mainly because of the presence of Latin script.
Arabic is poorly represented in every category, with less than 1% of IDN registrations.
We have discussed in previous reports the complexities inherent in using IDNs which mix scripts (for example Han script at the second level, with a top level ASCII/Latin script). Those complexities are most acute where IDNs are bi-directional, combining right-to-left labels with left-to-right TLD endings. The resulting names can be challenging to use, as the strict hierarchy necessary for domain names to work becomes confused.
For example, compare:
Given the popularity of traditional, ASCII domain names, it is to be expected that Latin script IDNs will be popular at the second level (under ASCII TLDs such as .com and .eu).