Final answer:
The term used to describe a temporary decline in thinking ability when using a less proficient foreign language is language interference.
Step-by-step explanation:
The term used to describe a temporary decline in thinking ability when using a foreign language in which one is less proficient than their native tongue is language interference. Language interference can occur when the structures or patterns of one language intrude upon the other language being used, causing cognitive difficulties.
For example, if a person's native language is English and they are less proficient in Spanish, they may experience language interference when trying to communicate in Spanish. They may struggle with grammar, vocabulary, or sentence structure, leading to a temporary decline in their ability to think and express themselves effectively in Spanish.