Why is it easier to understand English spoken by German, Scandinavian and Dutch English speakers than Indian English speakers? 

I m not a linguist but have dabbled as a CS and statistics person have dabbled in statistical NLP and CL.

 Indian languages, unlike most European languages, have more phonemes, more characters, more consonants, less diphthongs. For example, English has 13 diphthongs while Hindustani (Hndi, Urdu) has just 4. See forr example, <\p>

Low occurrence of Diphthongs seem to enable Indians speak their languages fast. And we speak any language, including English, fast. Secondly most Indian languages have many retroflex consonants that do not exist in English. I would also add a whole bunch of factors that make Indian spoken English difficult. I had already written about speed and diphthongs. I c1. an add four more, and they are entirely the result of lack of emphasis on them in Indian education. They are,

1. Pauses: It becomes difficult to understand Indian English because pauses between phrases, clauses, as well as punctuations such as commas, semicolons. It also makes spoken Indian English sentences runny.<\li>
2. Pronunciations of English letters. They are different for US and UK English; Indians are taught British English most of the time.<\li>
3. Aspiration of first sound in words. Indians pronounce the p sound in pick or paint with no aspiration.<\li>
4. English sounds that don’t exist in Indian languages. For example, the a vowel sound in bank, when written in Indian languages are pronounced as either ‘byank’ (ಬ್ಯಾಂಕ್ in Kannada) or ‘byink’ (बैंक in Hindi.<\li><\ol><\p>