Depending on your circumstances, some languages can be harder to grasp than others. If English is your first language, these languages are widely considered to be the easiest to learn how to speak, read and write.
Picture: The LEAF Project
For many years the Defence Language Institute (DLI) has worked with the Department of Defence to teach foreign language to the US military and Federal Agencies. Because they have been doing it for so long, they have managed to learn a thing or two about which languages are more difficult for native English speakers to learn. According to the DLI, these are the easiest languages in terms of how long it takes to become moderately proficient:
These four languages are considered Category I languages, and only take 26 weeks to learn enough to speak, read and write in the given language. Keep in mind, however, that those 26 weeks are intensive, so learning on your own could still take much longer. On the other hand, the difficulty goes all the way up to Category IV, with languages like Arabic, Mandarin Chinese, and Japanese taking at least 64 weeks of intensive training to reach the same level of proficiency.
If you're interested in learning a second language, it's certainly worth starting with some of the easier ones to see how you like it. Always be sure to consider what advantages learning a specific language will have for you, however. Learning Portuguese might be easier to learn, but if you're never going to use it, you might be wasting your time. You can learn more about the DLI's different language categories and difficulties at the link below.