There are two major roadblocks here, and I doubt either one will be resolved anytime soon.
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The game is packed with Valkyria’s own archive format, and while common VN archive tools look like they can probably extract the files, there’s nothing that supports repacking them. In fact, from a quick glance at VNDB, I don’t see anything that looks like a completed fan translation of a Valkyria title. Even if you wrote your own tool to re-archive the files you’ve extracted and edited, you might find that the engine’s encoding and font choices don’t lend themselves well to non-Japanese scripts, necessitating modification of the executable itself.
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There’s a general lack of translators with both the will and skill to write a decent translation, and machine translation is no substitute. For small bits of text, you can certainly get the gist through Google Translate, etc., but with anything more involved you’re kind of screwed. Machine translators don’t handle nuance very well, and unlike humans they’re pretty much incapable of retaining context from one text box to the next. You might be able to use something like Translation Aggregator to get machine translations from a variety of sources at once, then look at what they have in common to get a gist of what’s being said, but you’ll still end up with names being translated directly into English-equivalent words, and even half-decent puns will end up looking like nonsense.
If you just want to speed through and have a vague idea of what’s going on, you might be fine just trying to use Translation Aggregator with some sort of hooking tool. If you want anything better than that, you’d probably have to commission a translation and the tools to insert it.