As was explained in the previous post, each language poses a different level of challenge to those who wish to learn it, depending on various factors.
4. Syntax. Linguist theorist claim that human brains are wired into in the subject-verb-object structure, meaning that people instinctively expect and understand that order. Whether this is true or not, languages not bound by this order, i.e. those that use the case system require more energy to learn and understand but are much freer in terms of sentence construction. A comparison of English and Russian demonstrates this point. While English may have many words to learn, once the learner recognizes that a given word is a noun, it requires no more effort to process and apply that word. The writer/speaker can place that noun in that form in any place where that word as a noun can enter. For example, the form of the word shelf is the same in the following sentences: The shelf is not straight; Line up the shelf; The bottle is on the shelf. The caveat is that the order of words is vital importance and follows strict rules. You cannot randomly mix up them up without changing the meaning. By contrast, Russian, like other case-languages, places various suffixes to nouns depending on its function in the sentence or what the word before it. The meaning of all this complexity is that learners of the Russian language do not have the tools to understand or write a proper Russian sentence until they learn all six cases (which is still easier to do than the 19 cases of Finnish). So, students of Russian earn their rewards. On the other hand, once this skill is attained, it is hard to make an error in sentence construction since almost anything is allowed.
5. Roots. The rule in regards to learning a language is that the fewer roots there are, the easier the language. In other words, you get more miles (kilometers) for every word you learn. So, Hebrew, a non-developing language for so long, is extremely easy to learn in that perspective while English is simply hell. The other issue with roots is familiarity. To a certain point, being familiar with the roots from another language eases the process radically. English speakers generally do not struggle with Spanish because many of the words sound familiar. It can happen that too much familiarity brings confusion. I studied Italian for several years. I had to remember the spelling differences between it and French, a more familiar language for me. For example, the word and is et in French but e in Italian. The same issue might arise among speakers of Slavic languages, among others. It always helps to have some knowledge in advance.
6. Intonation and tone. All languages have intonations, the manner in which various kinds of sentences are spoken, i.e. statement, question, exclamation, etc. This voice control varies from language to language and country to country and presents the greatest challenge to mastering a language since it requires conscious retraining of your voice. For example, English has limited up/down waves when making a statement: I bought a car. There is almost no difference in tone between the first and last word. In Russian, with the equivalent sentence, the first word would have a normal tone but the volume would decrease until the last word almost disappears. French, by contrast, will resemble a sine wave pattern, up and down. In Italian, well, it would like an opera, to my ear at least. However, a far greater learning challenge is tone-based languages, such as Chinese. The same sound can have numerous meanings, all depending on the tone of the pronunciation. Small children pick up those tones quickly but most adults struggle to master them.
So, it should be clear that no language is a piece of cake in all aspects nor is any language impossible to learn. Natural talent can be factor but motivation, time and effort can overcome any difficulty a language can pose. Every language opens the world and its people. This investment is clearly worthwhile.