Picking a new language isn't just about spinning a globe. For an English speaker, learning German is a fundamentally different challenge than learning Japanese. The reason lies in linguistic distance—the degree of similarity between your native tongue and your target language. A shorter distance means a faster, easier journey.

The most straightforward way to measure this distance is through lexical similarity, which tracks the percentage of words that are similar in form and meaning between two languages. Since English is a Germanic language with heavy French (and therefore Latin) influence, it has footholds in multiple language families. It shares about 60% of its vocabulary with German, but only around 27% with Spanish.

Governments have been thinking about this for a long time. The U.S. Foreign Service Institute, or FSI, needs to train diplomats to speak new languages quickly and efficiently. To do this, they created a ranking system that groups languages into categories based on the average time it takes a native English speaker to reach professional working proficiency.

The FSI categories provide a clear roadmap for what to expect.

These hours aren't just about casual app usage. They reflect intensive, focused study. The takeaway is clear: you could learn Spanish three times over in the time it takes to learn Mandarin.

This data helps frame the central question: what is the language for? If your goal is to travel through South America next year, Spanish (Category I) is a high-utility, low-difficulty choice. If your company is opening a new office in Tokyo, the 2200+ hour investment for Japanese (Category V) might be unavoidable but worth it professionally.

A useful hack is to actively hunt for cognates—words that share a common origin. Recognizing that the English word father is Vater in German and pater in Latin (the root for Spanish padre) gives you free vocabulary. The more cognates a language shares with English, the faster you'll build a foundational lexicon.

But be careful. Languages that are very close can also create linguistic interference, where rules from one language bleed into the other. An English speaker learning both Spanish and Portuguese might constantly mix up similar-sounding words or apply the wrong grammar rules. Sometimes, a little more linguistic distance can actually help keep the languages separate in your mind.

So before you choose, weigh the cost against the benefit. Consider the time you have, your professional and personal goals, and how much of a head start your native English gives you. A strategic choice is the first step toward fluency.