Learn Spanish (Latin America): Deseaba que este proyecto beneficiara a la ciudad. - I wished that this project would benefit the city.

In English, we say "would benefit". But in Spanish, the verb desear expresses a desire, which triggers the subjunctive mood for the second verb. Because the wishing happened in the past (deseaba), that second verb must be in the past (imperfect) subjunctive: beneficiara.

How do we get the imperfect subjunctive form beneficiara?

To form the imperfect subjunctive, you always start with the "they" form (third-person plural) of the preterite tense. For beneficiar, that is beneficiaron. You drop the -ron at the end, leaving the stem beneficia-, and add the appropriate ending. Since este proyecto is an "it" (third-person singular), we add -ra, giving us beneficiara.

Why is there an a before la ciudad? I thought the "personal a" was only for people.

You are right that the "personal a" is mostly for people and pets. However, it is also used with places, institutions, or groups when they are treated somewhat like people. Because a city is an entity made up of people, Spanish speakers often use the a before la ciudad when it is the direct object of a verb like beneficiar.

Deseaba can mean "I wished" or "he/she wished". Do I need to add yo to be clear?