How does one use a single adjective to describe two or more nouns of different genders?

Question

I was translating something from English into Spanish and hesitated a moment as I contemplated how best to do it. The phrase was

Lists of Taiwanese counties and cities

I hesitated because I wasn't sure if I could write

Listas de condados y ciudades taiwaneses

using the masculine plural form for "taiwanés" to cover both nouns, somewhat similar to the practice of assigning masculine gender to a group of people even if only one male is in that group. I was about to just try to get on with it and simply write

Listas de condados y ciudades de Taiwán

which is what I consider a form of "writing around it," but then I thought better of it knowing that taking the easy way out is not a good way to increase one's knowledge of a foreign language (or anything else for that matter).

I did try to search for an answer for this using a number of different methods, but nothing I tried definitively answered this for me. At one point I was hopeful that the thread

Adjectives that modify more than one noun

might answer the question. Though the title was promising, the discussion that followed from that question didn't really answer this one here.

Thanks in advance if you know the answer to this.

Answer 1

Your answer can be found in section 3.2 on the Diccionario panhispánico de dudas. Below is a translation of the original text:

3.2. One adjective postposed to several nouns. When one adjective qualifies two or more coordinated nouns and is postposed to them, it is advisable to inflect it in plural and masculine if the two adjectives are of different gender: «Tiene el pelo y la barba enmarañados»¹ (Matos Noche [Cuba 2002]); «Apareció [...] vestida con traje y mantilla blancos»² (Hernández Secreter [Esp. 1995]). If the adjective agreed only with the second noun, there could arise some ambiguity because it would be possible to interpret that the adjective only applies to the nearest noun: vestida con traje y mantilla blanca (where both the suit and the mantille white or just the latter?). However, when both nouns are considered to form a unit of which each is only a part, the adjective can agree with the nearest one: «La gente de origen y habla francesa predomina en la provincia de Quebec»³ (Tiempo [Col.] 1.7.98).

To answer your question, taiwaneses is the right choice. If you are concerned about the cacophony of an adjective following a noun with which it doesn't agree, you can always change the order of the nouns so the masculine goes at the end, as proposed in the comments. That isn't necessary, though -- to me, taiwaneses sounds just fine in your sentence!

Interestingly, the rules change if the adjective is preposed to the nouns; in that case, the adjective must agree in gender and number with the first noun (La indispensable vigilancia y control nocturnos), except when qualifying people (los simpáticos Paco y Toni). When the conjunction used is o instead of y, the rules are similar to the ones mentioned for y:

Cada vez que mueren un hombre o una mujer viejos [...],toda una biblioteca muere con ellos⁴

When the conjunction o is used to establish an equivalence, however, the adjective is inflected in singular and agrees in gender with the first noun:

El aerógrafo o pistola usado debe ser adecuado al compresor⁵

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^{1: His hair and beard are tangled.
2: She showed up dressed in a white suit and mantille.
3: People of French origin and language are predominant in the province of Quebec.
4: Every time an elderly man or woman dies, a whole library dies with them.
5: The airbrush or spray gun used must be adequate to the compressor.}