The problems here for you are Father Fuentes are many.
1. You say Psalms has a particular definition or use for the term “this generation” but
you have not cited to any verse in Psalms that supports your theory. When people make a statement without citation, they are usually wrong, exaggerating, lying and/or trying to mislead. I suspect you are no exception to that rule.
2. I did your work for you and checked Psalms and was unable to find ever one occurrence of “generation” or “this generation” that supports your claimed construction of “this generation” as “people with a wicked mindset” or the “Jewish nation as a whole.”
3. The typical usage in Psalm had a temporal aspect. See Psalm 78:4 (“we will tell the next generation the praiseworthy deeds of the Lord”); Psalm 78:8 (“They would not be like their ancestors— a stubborn and rebellious generation”); Psalm 79:13 (“from generation to generation we will proclaim your praise. “); Psalm 109:13 (“May his descendants be cut off, their names blotted out from the next generation”); Psalm 145:13 (“One generation commends your works to another”).
4. Also note that even your two unsupported and inconsistent constructions – “people with a wicked mindset” and “Jewish nation as a whole” don’t preclude in any way a temporal aspect to the term “generation” depending on the context. We are analyzing the verse “Truly I tell you, this generation will certainly not pass away until all these things have happened” which is loaded with temporal context (“this” “pass away” “until” “have happened”) no matter what strained and unsupported construction you attribute to "generation."
5. To the extent you are suggesting something was lost in translation to English, I find that very hard to believe. There has probably been more analysis and scholarship of the Bible than all other books on earth combined. Surely one of the Bible publishers would have corrected “this generation” before. The Gideons? They were no slouches and a very detailed bunch. King James' guys? They were experts. They wouldn't blow an easy one like this.
5. “Truly I tell you, this generation will certainly not pass away until all these things have happened.” Plain English. Impossible for a literate person to misunderstand. It is clear as day that “THIS generation” is indeed the generation at hand that Jesus was speaking to. Not some other generation or some unbounded “generation” that includes some unidentified collection of endless generations of people of wicked mindset or a collection of Jews living from 0 AD to the present date (and beyond). Jesus was allegedly speaking to the generation then at hand. Not dozens of other future generations throughout time until today (and beyond).
6. Even C.S. Lewis said Matthew 24:34 was “the most embarrassing verse in the Bible.” He
believed Jesus was just flat out wrong. He was correct. Those words by Jesus were wrong. He was either mistaken, misguided, exaggerating or lying. He was wrong. Only a hopelessly biased zealot can hold out on that conclusion for very long. You and Father Fuentes have a lot of recalibrating to do.