In the specific case you ask about, español, if you are referring to the language itself, only español is valid, since you are referring to the Spanish language, and language in Spanish is masculine: "el idioma" or "el lenguaje".
If you are referring to the speaker, then you have unknowingly stumbled into a debate involving speakers of multiple languages with particular involvement of feminist and trans communities.
Gendered constructs arise naturally as a practical tool to narrow the possible set of denoted objects to half, halving the specificity of a sentence, examples:
"Jack and Jill met at the concert, she greeted him."
"La mesa me vino con un vaso. Lo tuve que tirar."
We can see in both of these examples that, since both subjects have different genders, the speaker can succinctly refer to them with just one pronoun.
The issue arises when the speaker wishes to refer to a group of possible subjects that include both genders, and they can only use gendered constructs to do so. In the previous cases, referring to both of the subjects in English is easy because the plural is gender neutral, they. But in Spanish, one cannot refer to both objects without specifying a gender. However, as we'll see, English still faces this issue in other situations.
I will be using the following examples as a study case:
"Engineer wanted; he or she should have experience in the automotive industry."
"Se busca ingeniero o ingeniera"
In English this debate takes form of gender neutral pronouns. As with Spanish, when the speaker wants to express an ambiguity in gender, but the syntactic rules require the use of a gendered construct, the masculine is traditionally used to denote both genders. The disadvantages are both practical and ethical - practically this creates an ambiguity, are we referring only to masculine things or both masculine and feminine things? The political implication is much more important and it concerns the introduction or expression of a gender bias when it might be detrimental.
If one does not wish to introduce a gender bias, either for practical or ethical reasons, there are a number of alternatives they could use. Each comes with their own tradeoff:
Language agnostic solutions
These solutions exist both in English and Spanish, and probably many other languages:
It is usually possible to alter the redaction of the sentence so that meaning is minimally impacted and the gender construct is avoided:
"Engineer with experience in the car industry wanted."
"Se buscan profesionales de ingeniería con experiencia en la industria de autos."
Gender neutral masculine
This is the traditional solution to gender-ambiguous words. If introducing a gender bias is not a concern due to practical or ethical reasons, the masculine
"We are looking for an engineer, he should have experience in the automotive industry."
"Se busca ingeniero"
The ambiguity in gender will generally be understood; the major tradeoff is that it can be disrespectful towards female audiences.
Note that using the female gender will convey an equivalent meaning, and will give the impression that exclusively females are being referred to.
Languages evolve; several competing language constructs have emerged in the recent era, notably championed by trans-inclusive movements in English and feminism in Spanish. In English, the gender-neutral plural pronoun they has gained adoption as a singular gender neutral plural (and has been in this answer); other more experimental and unambiguous variants include per, xir, etc. Spanish has a few of these constructs with varying levels of acceptance:
Gender neutral 'e' conjugation
The 'e' conjugation has been quickly gaining adoption in cases where both 'o' masculine and 'a' feminine suffixes are legitimate:
"Se busca ingeniere"
The legitimacy of this construct is hotly debated, but the fact that there is a hot debate usually means that there is widespread use and, at the very least, you will be understood. The major tradeoffs of this approach are intelligibility amongst non-users of the construct, risk of annoying politically conservative audiences; the major benefits are increased expressiveness among users of the construct.
at symbol '@' as gender neutral suffix
The at symbol has acquired many meanings since the advent of the internet; due to its similarity to both the o and a letter, it is widely used in written media as a gender neutral suffix:
"Se busca ingenier@"
The major tradeoff of this approach is that it only works in digital text media. One advantage is that it avoids feminist connotations and might be more widely accepted in audiences where feminism carries a negative register.
###Gender neutral x suffix###
Finally, similarly to the @ symbol, the x suffix can be used in analog text media. This carries a feminist connotation, and is either not possible or hard to pronounce.
"Se busca ingenierx"