2. A method, implemented in a computing system, comprising: assessing a user's comprehension of a plurality of target foreign language words corresponding to a plurality of base language words; producing, in response to the assessing, a mixed language text based on a base language text, the mixed language text including a foreign language word from the plurality of the target foreign language words substituted for a portion of the instances of a corresponding base language word from the plurality of base language words occurring in the base language text, the producing performed in processor; and presenting the mixed language text to the user.
2. A method, implemented in a computing system, comprising: assessing a user's comprehension of a plurality of target foreign language words corresponding to a plurality of base language words; producing, in response to the assessing, a mixed language text based on a base language text, the mixed language text including a foreign language word from the plurality of the target foreign language words substituted for a portion of the instances of a corresponding base language word from the plurality of base language words occurring in the base language text, the producing performed in processor; and presenting the mixed language text to the user. 7. The method of claim 2 , wherein the assessing includes: presenting to the user a plurality of questions about the content of a passage of text including at least the foreign language word from the plurality of the target foreign language words; receiving from the user a response to the plurality questions; and determining a proficiency datum associated with the user's comprehension of the target foreign language word based on the received response.