This is the 12147th most frequent Spanish word.
interponer
To place or insert between.
Here, "interponer" is used in a legal context meaning to formally lodge or submit (an appeal).
El abogado decidió interponer un recurso contra la decisión del juez.
The lawyer decided to file an appeal against the judge's decision.
In this context, "interponer" means to place an action (mediation) as an intermediary step before another action.
Es importante interponer la mediación antes de proceder con el juicio.
It is important to interpose mediation before proceeding with the trial.
Here, "interponer" is used to signify placing or inserting something as an obstacle or priority (personal affairs in this case).