This is actually a feature of the writing system, the orthography, rather than the language itself. Some languages have multiple writing systems or have changed writing systems over the course of history; an example of the latter is Korean, for which the Hangeul writing system was created in the 15th century.
How close the written representation of a word is to its pronunciation is sometimes referred to as "orthographic depth", with orthographically "shallow" languages having a closer relationship between the two, and "deep" languages having more complicated one. Other terms used are "consistent/non-consistent", "regular/irregular" or "transparent/non-transparent" orthographies.*
Usually a simpler writing system doesn't result from pronunciation somehow being derived more directly from the spelling of words. That's because in any language, the pronunciation of the most common and important words isn't derived from the spelling at all, but from oral transmission. Pronunciation based on spelling is a much smaller influence, which usually only occurs for fancy or scholarly words that people learn later on in their lives.
Instead, a simpler writing system usually indicates a younger orthographic system, or one that has been adjusted recently to make it reflect the pronunciation in a relatively direct manner. For example, the reason the current system of Japanese kana is so transparently related to the pronunciation is because they were reformed in 1946, replacing a more complicated older system that was based on the historical pronunciation of words. On the other hand, English spelling has changed rather little since Samuel Johnson's dictionary of 1755, and many proposed comprehensive spelling reforms have failed to catch on.