Many languages have inflectional or agglutinating morphology - they have words with multiple or many forms due to aspect, degree or comparison, gender, mood, number, tense, etc.
A number of languages do not indicate boundaries between words in their written form. I include in this category languages which indicate boundaries between all syllables. The languages of this type I know of are Burmese (Myanmar), Chinese, Dzongkha, Japanese, Khmer (Cambodian), Lao, Thai, Tibetan, and Vietnamese. Plus a number of minority languages of Southeast Asia such as Mon and Shan.
Please note that I am only asking about inflectional morphology and not about derivational morphology or compounds.
Segmentation for languages without word boundaries presents a challenge to natural language processing due to ambiguity. Lemmatization of inflected forms is also a challenge due to ambiguity.
The only language I can think of for which NLP must tackle both these problems at once in Japanese. But are there any others I've overlooked?