So how should one measure the difficulty of a language? This would be a matter of great debate, but one might start with grammar. But even within grammar there are a number of different considerations.
Firstly there are usage considerations. This could bleed over into cultural differences and not merely linguistic, but it bears a mention. Specific rules for being indirect, politeness, formalities, etc. can lend a huge difficulty for foreign speakers. So for example, a language with complex rules for politeness such as Japanese, would be on the harder end, and a language in which polite forms are not widely used (such as English) may be considered easier.
The sound system of a language is another element of difficulty that could be ranged on a scale. Hawaiian is one of the most simple languages, phonetically speaking. It only has 13 distinctive sounds (phonemes): eight consonants and five vowels. Due to strict grammatical rules, these can only be combined into one consonant and one vowel (usually) and there are only 162 possible syllables. Compare this to a language on the other end of the spectrum, such as the Khoisan languages (also known previously as Bushman) spoken around Africa. Some have up to 156 distinctive sounds, many of which are types of clicks. These would be considered on the far end of the difficulty spectrum. Clearly it would be much easier to learn the pronunciation of Hawaiian than the Khoisan languages.
What about the writing system and orthography (rules for spelling)? Obviously this can be a matter of perspective and relativity. Learning a different alphabet would raise the difficulty for certain language speakers who must step outside their native alphabet. There can be levels of difficulty even within an alphabet, as certain languages have more complex orthographies. English, for example, is fraught with silent letters and syllables that make no sense. Spanish is a bit more orthographically simple as pronunciation is much more uniform. However the two use the same alphabet with a couple variations.
But even within the confines of certain grammatical elements, languages are not uniformly simple or difficult. One could compare English to Finnish and say that Finnish is simpler because there aren’t any articles. But then one could turn around and say that the elaborate system of Finnish inflections on nouns makes it more difficult than English.
Or compare English to Maori. Maori requires that a noun can only have one adjective modifying it at once. So in order to say “I saw a big red truck” you would have to say “I saw a big truck. It was red.” Is that harder or easier than English? Harder because it uses more words? Easier because there’s one thing going on at a time? There’s really no way of saying in a quantifiable manner.
So you see the answer of whether or not one language is more simple or easy than another is not one that is easily quantified. All languages have their easy and hard points. The subject of the hardness or difficulty of a language could be chopped up into so many different elements, and even within these elements it’s hard to define levels of difficulty because one is always working from the perspective of his or her own native language.
“Language Myths”, Laurie Bauer and Peter Trudgill