Besides being a study abroad junkie, I love learning new languages and mastering my current ones, of course. I have a lot of experience in romance languages (esp. Spanish and French), speak English as my native tongue and have a fairly decent command of Arabic (الفصحى) and Japanese. I’ve always heard that learning a new language is supposed to get easier the more that you learn, however, I’ve found the opposite to be true. While French wasn’t particularly more difficult than Spanish, Japanese was infinitely harder than French and Arabic has proven to be the stone upon which I beat my head bloody.
On the other hand, the difficulty with these languages has arisen because of vast differences in the languages rather than similarities. For example, going from the Latin alphabet of English, French and Spanish to Japanese was very difficult. However, after learning kanji, katakana and hiragana, the Arabic alphabet was relatively easy to learn. Distinguishing the different sounds in the Arabic alphabet has proven rather difficult as there are many sounds that we do not distinguish between or produce in English.
French grammar is very similar to Spanish grammar which in turn is not very different from English. In retrospect, the grammar of these two languages was very easy to learn in comparison to that of Japanese or Arabic. Japanese grammar is straight-forward but confusing at first because of its differences compared to Indo-European languages. Arabic grammar, on the other hand, seems to be anything but straight-forward. For every rule that is learned, there seems to be an endless array of rules that counteract or slightly change the first.
Overall, I think that learning another language becomes easier the more you do it, but each language has unique challenges for the learner. Also, the more fluent you become in one language, the harder it can be to start learning another. After I became fluent in Spanish, learning Arabic became difficult as I often wanted to use Spanish words and grammar in place of Arabic. However, over time this difficulty subsides and it becomes easier to separate the two languages.