I was poring over the spell list in the Moldvay Basic rules, pondering a few posts, maybe a series, on under-utilized spells. Perusing the description of the humble 1st level magic-user spell read languages, a thought struck me about the style of gaming for which those spells were originally designed.
So, when would a player choose to prepare or cast read languages? The obvious answer, of course, is when the DM is running the type of game in which the player stands to gain something by doing so. I think that type of game is either a true sandbox or one with a predominance of sandboxy elements.
Consider first a fairly linear, plot-driven adventure. Because the adventure setting and other details are probably going to be used only once, anything extraneous to the plot is likely to be pretty thin, when present at all. Writing up descriptions for locations, dungeon rooms, NPCs, etc. that aren't related to the plot is just extra work for the sake of work. The dungeon won't have many rooms that don't contain something important to the adventure. Major obstacles are usually essential to the plot, choke points that must be surmounted in some prescribed fashion in order to proceed. If there's a door marked with ancient runes or a scroll with an encoded message, it's never superfluous or tangential to the plot. It's there to advance the PC party toward the final resolution of the quest.
For that reason, it's pretty rare that the author of such an adventure would include those things without also including the means for deciphering them. The adventure must not hinge on the players having access to a particular spell at a particular point. It must not come to a grinding halt, or even end in failure, for want of a magic-user who knows and has prepared read languages. Instead, the author will generally drop in some sort of plot coupon - a Rosetta stone, a mislaid copy of the cipher, an NPC who knows the ancient language, or (completely lacking imagination) a scroll containing the spell in a chest nearby.
Savvy players will pick up on this, and realize that it's mostly pointless to prepare or cast read languages. Search for the plot coupon, and save those precious spell slots for slinging magic missile and sleep spells during the inevitable climactic set piece battle. It is possible, of course, that the price of winning the plot coupon is greater than a first-level spell, and it would make sense to circumvent it with a quick casting of read laguages. Given the tendency of that type of adventure toward railroading so that
No Encounter is Wasted, though, it's likely that the author will contrive some reason that read languages won't work, requiring the party to go through the encounters to get the plot coupon. (If you really want to discourage players from preparing utility spells, make those spells useless in any situation that significantly advances the party's goals because it interferes with somebody's conception of a good story.)
Compare that to a sandbox campaign, in which a large dungeon complex or wilderness area may be the scene of multiple adventures, whether they're simple dungeon crawls ("Why? Because it's there!") or quests to accomplish some particular goal. There are multiple paths by which any given location may be reached, and many features that aren't essential to any plot. They're just there to be discovered and utilized in whatever ways the players can conceive.
In this sort of environment, players have no assurance of plot coupons to get them past obstacles without expending resources, nor do they automatically know which things they encounter are relevant to their current quest and which aren't. If they want to read the message on that door, engraved in strange glyphs of the forgotten tongue of the Old Empire, they can search the dungeon high and low for some secret decoder ring that may or may not exist, they can make a rubbing of it and take it to a sage in town, or the party magic-user can zap it with read languages and find the answer right away, without further waste of precious time. They can also choose to move on and forget about it. The most important consideration is that the success or failure of the adventure doesn't hinge on their reading the message. It's not a choke point which must be passed to advance to the next stage; it's one piece of a puzzle, and the players might still be able to make out the overall picture without any given piece. Because the possibilities are so wide-open, there's no need to ensure that the party can read it even if they don't have a spell, and no reason to prevent the spell from working to preserve anyone's idea of how the story should progress.
Reading the message might allow the party to claim any number of advantages. Perhaps it forewarns them of hazards, or gives access to a shortcut that bypasses those hazards. Maybe it points to a magic sword or a potion that could be of use in this or future adventures. Maybe it's a map of part of the dungeon, or a misdirected message that discloses parts of the villain's plans that a clever party can exploit. Maybe there's a hook for a future adventure. Maybe there's bonus loot to be gained. Maybe there's something unrelated to the current mission that reveals interesting information about the dungeon or other features of the campaign setting. Or maybe it leads to a monster or trap that deplete their resources. There's risk involved, after all.
Of course, all of this is moot if you don't liberally salt your setting with books, scrolls, engravings, heiroglyphs, ciphers, and other written material and make at least a fair bit of it helpful and relevant to the party.